Does a builder need a certificate to guarantee work

We've never been asked for money up front.

I own and run a renovation business and I would say depending on the amount of work and materials required I would ask for a 50% deposit for job that is costing €1000’s.  Smaller jobs then I wouldn’t always ask but I also would give you a formal quotation which would outlay a deposit required/recieved.  This is normal in any country.