The most important thing is do avoid handing over cash or paying large sums in advance. Be wary of paying cash for a cheaper job, i.e. to avoid VAT, you may be going down a slippery slope of not doing things properly which may eventually mean your job is also not done properly.
Agree when you intend to pay, ideally after you are satisfied with the completed job. If it is a big job agree a schedule of staged payments which is fair to both parties.
To avoid bad tradespeople and to ensure you can find them should they not answer a mobile;
- Get proper contact details and check them yourself
- Check if the company is verified on the Companies House website
- Get phone details, ideally a land line or 0800 number and check it
- Get a physical office address