Check references thoroughly. Ask for at least three references from previous clients and actually call them. If a contractor is hesitant to provide references, that's a red flag.
There are also stories where contractors work on large commercial projects. They might face challenges in coordinating with different teams, like the electrical and plumbing teams. A contractor once told me how he had to reschedule the work of all the sub - teams when there was a delay in the delivery of building materials.
There was a contractor we hired for building a small patio. He seemed very professional at first. He started the work but used really cheap materials instead of the ones we agreed on. When we confronted him, he got really defensive and started yelling. It was a nightmare. We ended up having to pay someone else to fix the shoddy work he did.