contractor and wholesaling

[Jawad Ihmoud]

I am very confused when it comes to getting estimates from contractors. My idea of it is that I would call several contractors and have them estimate (bid) how much everything, such as rehabbing would cost, but do I pay them and those who do it for free how do they get awarded? I am asking this since I would be wholesaling and so I would not know who the buyer would want to use as a contractor. Also, how much should a contractor be paid for estimates? As well as, how do I know the contractor is accurate in his estimates?

Thank you