How do you pay GCs/contractors?

[Beste Park]

Hi! I'm relatively new to flipping in the US and don't have much experience with estimating construction costs.

New flippers, how do you solve this challenge? Do you bring a general contractor (GC) every time you do a walkthrough and get different bids during the inspection period? If yes, do you pay (and how much) the GC for the initial walk?

I would love to hear your insights! Thanks.