This request for an advance payment of 50% is far beyond any normal trading practice. The only situation where you might consider making any advance payment at all would be if the builder was well known to you, lived locally and was a one-man firm or similar. In that case it may be worth considering, but you should not simply hand over a cheque; the money would probably be for materials so the best thing would be to open an account in your name at a local builders’ merchant with a stated limit for the builder to use. In that way you would retain ownership of the materials and know the money was not being used for other purposes. The danger is that your builder may be in financial difficulties and would use your advance to pay off old debts to keep trading and then might not be able to finance your job. This sounds extreme but it does happen. The problem is that it’s often hard to find builders these days and you may be reluctant to risk losing him by taking a hard line, particularly if you know him. So your suggestion of 10% advance plus interim payments may then be an acceptable compromise. As for retaining money until you have checked for defects, in larger building contracts it is normal to retain 5% from interim payments dropping to 2.5% on completion and paid off in full three or six months later.