Put together good numbers. It's that simple.
It's common that in every market, investors have dealt with wholesalers that increase the ARVs and decrease the repair costs in order to make the deal look more appealing to someone that can't point out the difference.
In order to be a great wholesaler you have to first understand two of your most valuable skills: negotiations, and marketing.
First and foremost, you have to understand the needs of your clients. This is the seller and rehab buyer. Obviously there are details about the seller that you need to know in order to piece together a good deal for your buyers. Go into every deal as if you were going to rehab it. Run the numbers and come up with your own ROI or profit. If those numbers are what you would want as a rehabber, then that is your starting point. Anything lower than that, is your "wholesale fee". Obviously the numbers are going to dictate a lot of this in how far you are willing to negotiate, and you have to be reasonable to the seller. Remember, if one person loses in a deal, it's not a deal.
My point being, if you are a rehabber and are negotiating with sellers, you have to be good. If you are a wholesaler, you have to be better. You cannot, as a wholesaler, buy properties at a price that would only work for a rehab and try to wholesale it.
Be honest with yourself when running numbers, because this can make a huge impact on your reputation.
If you need to hire contractors to give you quotes to estimate repairs, do that. While you're at it, in your wholesale presentations, add their contact info. You're helping out everyone in the process. As for calculating ARVs, if you're unsure about that, learn from someone who knows how to do this, or ask a realtor. This is free information.
Lastly is marketing. Put together something that is attractive to the eye, a one page document that takes only seconds to look over. Only show the basic information (Neighborhood or Zip code, Purchase price, rehab cost, ARV, and comps. If you are running numbers as a rental, then add those in there as well). If someone is truly interested, they will ask more questions.
At the end of the day, as a wholesaler, you have to ask yourself: "Would I take this deal if I am unable to sell it?"