How to check if a builder is good?

You check if a builder is good by looking at their work after a year of use, not the week it was handed over. Fresh paint flatters everyone. Ask to visit a job the firm finished last winter and see whether the doors still close, the tiling is still tight, and whether cracks have run off the corners of new openings. Any decent firm has past clients happy to show you round; we take people to jobs in Sydenham and Bromley that are two or three years old for exactly this reason.

While you are there, look at the detailing, because that is where good and average separate. Skirting scribed to a wonky Victorian floor rather than caulked over a gap. Tile lines that carry straight through a corner. Silicone in one clean bead. Paint cut in sharp against the ceiling. None of this is decoration; it tells you how the same hands treated the joists and the damp course you cannot see.

Then ask the owner about snagging. Every job has snags, ours included, so the question is never whether there were problems but how fast they were dealt with and whether the phone still got answered after the final invoice was paid. A builder who came back twice without fuss is a good builder. Paperwork checks before you hire are a separate exercise; this is about proving the workmanship itself.