What should you not say to a builder?

Never say 'just do whatever's cheapest', and never offer cash to dodge the VAT. Those two sentences do more damage to a job than any amount of bad weather.

'Whatever's cheapest' sounds like flexibility but it is an instruction, and a builder under time pressure will follow it: the thinnest plasterboard, the bargain shower tray that leaks within a year, the paint that needs doing again in two. You have told them corners do not matter to you, so corners get cut. Say instead: 'here is my budget, tell me where it is tight and what I should not compromise on'. That gets a builder thinking with you rather than past you.

The cash-for-no-VAT offer is worse. Set aside the legality; you have just told your builder you are comfortable with things off the books, and you have given up the invoices and paper trail you would need if the work goes wrong. In our experience the firms that take that deal cut other corners too, because you have shown them where the bar is.

A few smaller ones. Do not open with a speech about how your last three builders were all crooks; it tells the good ones you will be hard work. Do not keep waving the other quote around after you have signed. And do not promise fast decisions then sit on tile choices for three weeks, because programme slippage sours a job faster than money does. Be straight about budget, priorities and timing, and you will get the same back.