Right Time To Bring Contractor-Wholesale

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Ok. I'm green to this wholesaling thing. I found a house selling as is. In trying to apply 70% rule of course I can't because I don't know what are the repair costs and all yet. My question is this. When is it the right time to bring a contractor in(since I cant come up with estimates on my own just yet)? I haven't talked with owner or anything just yet but when the owner does invite me to see the house and we negotiate a price do I bring a contractor with me AFTER I meet with owner or how does that work?