I thought of an example just a minute ago...my wife's car needed a bit of body work and my neighbor recommended a body shop.
I took the car there and we talked, he showed me his work (and it was good) so we talked about getting the car done...he told me to drop it off on a Sunday and leave the keys in a drop box and he'd get at it Monday morning. I said I would and where was the paperwork?
He said he doesn't use paperwork-it's all word of mouth with him. I told him I'd be taking my car elsewhere then...I also told him having an agreement protects him as well as the customer, if either party goes into a chapter 11 scenario, the bank could come and seize the vehicle and he'd be out his money, with a signed agreement, he'd become one of the lien holders and would be entitled to a pay out...on the other hand, if something happened to him and the work couldn't be done, the customer would have grounds to go get their vehicle without it being seized.
If I was getting expensive work such as a turbo system put on my bike, it wouldn't leave my driveway without a proper agreement being signed.
As our new member
@OldFartDave said, "trust nobody" and you'll be good....