Question about contractor estimates

[Rebecca Clements]

I'm wondering where in the process you bring in a contractor for an estimate whether that's for a flip or a rental property that you need to rehab. My issue is that I'm getting sent great deals each week but can't find any good contractors that will meet with me quick enough to look at the property before someone else already makes an offer. Is it better to make an offer before getting the estimate if you have a good enough idea of what the rehab might cost? It's just really frustrating because I keep missing out on good deals.

Also, I did have one contractor tell me that they charge for estimates. Is this common? I can understand them not wanting to waste their time. Just wasn't sure if this was common practice or not. 

Thanks in advance!