I built a WhatsApp + voice AI agent in n8n that handles 90% of customer service. Sold the business, the buyer kept it running without me
I owned a device repair shop for 16 years. I was losing 80+ hours a month answering the same WhatsApp messages: "how much to fix my screen?", "when can I pick it up?", "do you have this part?"
So I built an AI agent that handles both WhatsApp and voice calls. It's been running in production for over a year at <€200/month.
What it does:
Customers message on WhatsApp or call the shop. An n8n router classifies what they need and routes to one of 4 specialized sub-agents:
- One books appointments by checking real availability and confirming the slot
- One gives accurate quotes by looking up the actual device model and repair type in the database
- One checks stock in real-time and places internal orders when parts are missing
- One escalates to a human with full conversation context when it can't handle something
The voice channel goes through ElevenLabs. The sub-agents don't care if they were triggered by text or voice — same logic, different entry point.
What surprised me:
The "dumb" decisions mattered more than the AI:
- Using a different model per agent saved a lot of money. The booking agent doesn't need GPT-4 — a fast cheap model works fine for parsing "next Tuesday at 3pm". The quote agent needs accuracy so it gets the better model.
- Pseudo-streaming on WhatsApp made a huge difference in perceived speed. Instead of sending one long message, I split the response into sentences and send them one by one. Users see typing indicators and feel like they're talking to someone.
- The think tool on the router (making it reason before picking a tool chain) cut errors by roughly half.
- Airtable as single source of truth meant the agents were always working with real data — prices, stock, bookings. No sync issues.
Results after 12+ months:
- ~90% of interactions handled without a human
- ~80 hours/month freed up
- Running cost: <€200/month total
- Response time: <30 seconds
- Available 24/7 instead of just store hours
The real test:
I sold the business in 2025. The buyer had zero technical knowledge. All the AI systems — the WhatsApp agent, the voice agent, the automations — kept running without me. That's when I knew the architecture was right.
What I'd do differently today:
- Claude instead of GPT for the router. Better at structured tool calling in my experience
- Observability from day 1 instead of relying on n8n execution logs
I open-sourced the workflows if anyone wants to look at the actual implementation. Happy to answer questions.
Workflows: https://github.com/santifer/jacobo-workflows