For years, businesses have debated whether to focus on search engine optimisation (SEO) or paid advertising. Some believe SEO is the only sustainable route, while others argue that paid campaigns deliver the quickest returns. The truth is that both are essential, and the real power lies in combining them.

At Castle, we help ambitious eCommerce businesses grow by implementing strategies that use SEO and paid advertising together. This dual approach delivers compounding returns: SEO builds long-term visibility, while paid ads provide immediate sales. By aligning the two, brands can achieve higher ROI than they ever could with just one channel.

The role of SEO in eCommerce growth

SEO is the process of optimising your website so it appears higher in organic search results. For eCommerce businesses, strong SEO ensures products are visible when customers search for them.

The benefits of SEO include:

  • Sustainable growth: Once rankings are established, they can deliver traffic for years.
  • Credibility: Customers trust brands that appear at the top of search results.
  • Lower long-term costs: Organic traffic reduces reliance on continuous ad spend.

However, SEO is a long-term investment. It takes time to build authority, create content, and earn rankings. This is why many businesses give up too early or fail to see immediate results.

The role of paid advertising in eCommerce growth

Paid advertising offers the opposite benefit. Campaigns on Google, Meta, or Amazon can deliver results almost instantly. By targeting the right audiences, brands can generate traffic and sales within days.

The benefits of paid advertising include:

  • Speed: Immediate visibility and sales.
  • Control: Budgets, targeting, and placements are entirely customisable.
  • Scalability: Campaigns can be scaled up once proven profitable.
  • Measurability: Every click and conversion can be tracked.

The challenge with paid advertising is sustainability. Costs increase as competition rises, and campaigns need ongoing optimisation to remain efficient. Without strong site performance or brand authority, ROI can stagnate.

Why combining SEO and paid advertising works best

The strongest eCommerce strategies do not choose between SEO and paid advertising – they combine them. Here’s why:

  • Short-term and long-term balance: Paid ads deliver quick wins, while SEO builds lasting traffic. Together, they provide immediate revenue and long-term stability.
  • More customer touchpoints: Customers rarely purchase after one interaction. Seeing a brand in both ads and organic results increases trust and purchase likelihood.
  • Data sharing: Paid campaigns reveal what keywords convert best. That data can guide SEO strategies to target the highest-value search terms.
  • Cost efficiency: As SEO begins to deliver organic traffic, reliance on paid spend can be reduced or redirected to new growth areas.

This integration creates a compounding effect. Businesses grow faster, and ROI increases across the board.

Case studies that show the power of integration

Castle’s work demonstrates how combining SEO and paid advertising drives stronger results.

  • Geepas: We rebuilt their eCommerce store with better UX (a critical part of SEO performance) and ran targeted ad campaigns across Google and Meta. The result was a 126% increase in sales, a 57% rise in conversion rate, and a 7.02:1 combined ROAS. Without optimised site performance, the ads would not have delivered the same ROI.
  • Nicholas Charles Fragrances: Through targeted Google and Meta campaigns, we achieved a 72% increase in sales in 30 days. At the same time, SEO improvements strengthened the brand’s credibility in search results, helping conversions increase by 239%.
  • Fizzy Whiz: By rebuilding their Shopify store (improving SEO fundamentals such as site speed and functionality) and running campaigns across Google and Meta, we delivered ROAS figures above 10:1 and an 82% increase in overall sales. Paid ads worked because SEO foundations were strong.

Each case highlights the same lesson: paid advertising and SEO are not rivals – they are partners in driving growth.

The customer journey in 2025

Modern customers shop differently than they did even five years ago. A buyer might see an advert on Instagram, search for reviews on Google, and then complete their purchase on Amazon. Rarely is the path to purchase linear.

This means businesses need visibility across multiple touchpoints. Paid ads introduce the brand, while SEO reinforces credibility during research stages. If a brand only invests in one, they miss customers at key moments. By combining both, businesses capture more opportunities throughout the journey.

Why data makes the difference

One of the biggest advantages of integrating SEO and paid advertising is the ability to share data.

  • Keyword insights: Paid campaigns reveal which search terms convert best. This data informs SEO content strategies.
  • Audience behaviour: Paid ads provide demographic and behavioural insights, which can shape organic content.
  • Conversion tracking: By analysing data across both channels, businesses can see where ROI is strongest and adjust budgets accordingly.

At Castle, we track the entire funnel, from first click to repeat purchase. This data-driven approach ensures budgets are directed to the most profitable areas.

Avoiding the trap of treating SEO and paid ads separately

Many businesses still treat SEO and paid ads as completely separate functions, often run by different agencies or teams. The problem with this approach is that opportunities are lost.

For example, an ad campaign may reveal a high-performing keyword, but if the SEO team does not act on it, the long-term benefit is wasted. Similarly, SEO content may generate strong organic traffic, but without retargeting ads, many potential customers leave without converting.

By managing both together, Castle ensures every opportunity is maximised.

Why a full-service partner matters

Running SEO and paid ads in silos creates inefficiency. A full-service digital marketing partner brings both under one roof. At Castle, our specialists in SEO, paid media, and eCommerce web development work side by side. This ensures strategies are not only aligned but also constantly refined using shared data.

Clients benefit from:

  • Faster results through coordination.
  • Stronger ROI from budget allocation across channels.
  • Seamless strategies that cover both acquisition and retention.
  • Accountability from one partner managing everything.

This full-service approach is what allows us to deliver results like 277% sales growth in 90 days and ROAS above 10:1.

Building a sustainable growth engine

The future of eCommerce lies in building growth engines that deliver both immediate sales and long-term stability. Paid advertising fuels rapid growth, while SEO builds authority and reduces reliance on continuous ad spend. Together, they create sustainable momentum.

At Castle, we help clients build these engines. By aligning SEO and paid advertising, supported by site optimisation and data analysis, we deliver strategies that scale consistently.

Businesses that invest in both will be the ones leading their industries in 2025 and beyond.

Book a free consultation with Castle today and learn how combining SEO and paid advertising can maximise your eCommerce ROI.