Mattylad you forgot 'free use of the phone'
Ask and expect a written quotation for a start and not an 'estimate'..a quotation is more of a fixed price.
Ask him to itemise the work you want doing so your both clear on whats to be done..and equally important whats NOT to be done.
Dont ask him to separate labour and materials, it can put some peoples backs up...after all, your more or less asking him what he earns.
Agree payments, how much and how often.
If he says he needs money up front for materials..ditch him, any tradesman worth their salt should have a credit account.
Ask what needs to be moved...nothing worse than walking into a job and the customer hasnt bothered to shift a thing ..you often get the 'i forgot you were coming'...yeh right, they wouldnt have forgot if you hadnt have turned up beleive me!..in customer speak this means 'im paying you..you move it'
Make sure he or she has insurance and ask to see it, again a decent tradesman will offer it.
Haggling..its up to you, personally you might be better to tell the builder you want a straight price, no knock odwn discounts on the night, no gettng back to you with a better deal or matching someone else price..explain to them that you have told the other people quoting for the job the same thing. If they say '£xx.xx how does that sound' on the night they are probably waiting for you to knock them down, thus..thy have 'stuck a bit on'..just say you'll let them know.
For my part, if a customer asked for money off I would either say no..or not do the job, some people just have to have 'a deal' I have have given people a price of say 500 quid and the first thing out of their mouths is 'what about 400'...not even knowing what I was going to do for that price..
Qualifications...hmm..I know loads of great trades people who have never set foot in a college and loads of lousey ones who have qualifications coming out of their ears...
Go with the quote and the person you feel most comfortable with..not the one who is the cheapest.
Look for trade association memberships and check them out with that association..dont take their word for it..there are thousands of tradespeople out there who claim to be member of vairous assocications and aint..
Good luck