Contractor always does work without contract, problems for me

[Allen L.]

for the past year I’ve worked with a contractor on most of my rehabs, we signed contract for the first 1 or 2 projects and all later projects he would just send me an invoice to pay X amount to start and the remaining on finish. I consider this a verbal agreement but of course there are no fine prints. 

I get the feeling it’s more problematic for him. What sort of common legal problems am I exposed to because I don’t have a contract on every project?