Why not always buy wholesale?

[James De Silva]

There is a lot of information out here on how to become a wholesaler, but I can't see as much for people who want to buy and hold properties at the best price. Would I be correct in saying the following?

A wholesaler will find properties which are undervalued and get them under contract to be sold to an investor or a rehabber. They want to maintain good relationships since buyers often come back to them, so they might "buy" a property thats 70% below market, and "sell" it to the investor at say 85%. Then both parties are better off.

Whilst this is similar to a realtor, a wholesaler isn't as constrained about what they can say about the property.

1) If this is true, why would anyone who is in the property investment business buy from a realtor?

2) Can landlord investors profit from wholesale purchases or is it only those who rehab and resell?

3) I'm sure wholesalers can be found at REIAs, but what's the best way to determine who is worth doing business with? (Note - For anyone who wants to give referrals, I'm in the Metro Detroit area)