Our neighbour had his patio re-grouted and was pleased with the finished result. it did look good, so we asked the contractor to quote to re-grout our (much smaller) patio. He gave us a quote and asked us to pay for the materials in advance. In the meantime, he finished our neighbour's job and there were four tubs of grout left over. He sold them to us at a reduced price to avoid the trouble on returning them, which would have involved a courier/pallet.
It was a couple of weeks before work on our patio started. In that time, we found the same grout at a cheaper price from a different supplier and told the contractor we would buy it. (He wasn't making a profit on the materials.)
Anyway, the job has now been completed and we're left with unused five bags and four tubs of grout - worth around £250 - for which we have no use.
The chap who did the work is in his early 20s and has recently started working for himself. His work is good, but is estimating is clearly way out.
We have his final bill for £275 labour. If we pay it in full, we will be £250 out of pocket. Would be interest to know what other people would do in this situation, please.