A marketing agency is worth it when (1) marketing is not your core competence, (2) you can't justify a full-time hire (in-house team typically £55k–£180k loaded vs agency £3k–£15k/mo), (3) you need multi-discipline expertise faster than hiring allows, (4) ROI is 3–10x within 12 months. Not worth it when (a) you have product-market fit problems agencies can't solve, (b) you have monthly spend below £500 (signal too thin), (c) you're hiring an agency to avoid making strategic decisions yourself.
Sub-£5m revenue: agency. Marketing is critical but not core; can't afford full-time senior hire. Agency gives you senior strategy at fraction of in-house cost.
Multi-discipline needs (web + brand + SEO + PPC + content): agency coordinates across disciplines under one accountability. Hiring 5 freelancers requires 5 management overheads.
Specialist needs your team can't develop: Klaviyo Master, HubSpot certified, Shopify Plus partner, Google Ads expert. Specialist agencies bring depth your generalist team can't replicate.
Above £5m revenue: in-house team starts paying back. Loaded cost £55k–£180k per role; for £15k/mo agency you could hire a senior generalist + 2 mid-level specialists.
Brand-critical work (founder voice, content production, community management): in-house authentic voice usually wins agency-produced content.
Customer-data-sensitive work (subscription churn analysis, deep product analytics, customer interviews): in-house has more context and faster cycles.
Above £2m revenue, hybrid (in-house growth lead + 1–2 specialist agencies) wins for most. In-house lead handles strategy, vendor management, and brand-critical work. Agencies handle channel-specific execution.
Common hybrid: in-house head of growth (£90k loaded) + SEO retainer (£1,500/mo) + PPC retainer (£1,500/mo) + content writer freelancer (£2,000/mo) = £144k/year for senior strategy + 3 specialist channels.
"Hiring an agency to avoid making strategic decisions yourself. Agencies execute strategies; they can't replace your judgement on positioning, audience, and product."
Agency retainer £3,000/mo. Plus media spend £3,000/mo. Total cost £6,000/mo = £72,000/yr.
For B2B SaaS £3k ACV: need 24 customers/yr to break even (1:1 ROI). 48 customers = 2x. 96 customers = 4x. Realistic 2x–5x within year 2 once compounding kicks in.
For e-com £80 AOV: need 900 orders/yr to break even. 2700 orders = 3x. Realistic 3x–6x within year 2 with retention layered in.
Won't quote without 'discovery workshop' fee. Promises specific results month 1 (no real agency does). Refuses references. Charges minimum 6–12 month lock-in. Owns your code/Search Console/Klaviyo accounts. Reports vanity metrics not revenue.
Walk away from any of these. Plenty of legitimate agencies exist that don't pull these moves.