New to subcontracting - need advice

[Erenik Meka]

i'm working on rehabbing a townhouse and need advice on using a subcontractor. I've found someone willing to do the painting but need to know how to go about this. Some questions i have are:

-what do I need to know before hiring the subcontractor to do the work?

-what should I request or acquire up front?

-what do I need to provide him with? 

-how to determine if his quote on cost is legit?