@James De Silva
1) If this is true, why would anyone who is in the property investment business buy from a realtor?
Investors can still find good deals via realtors aka the MLS. Everyone that lists their property on the MLS is motivated to sell, some more than others. Buying property through a realtor is easier & less expensive because they don't have spend time & money on marketing to find these "extra motivated sellers". Banks also use realtors to sell their foreclosures- investors want to buy foreclosures. The same applies with a short sale.
2) Can landlord investors profit from wholesale purchases or is it only those who rehab and resell?
Yes, landlord investors can profit from wholesale deals. Wholesalers market properties as rehabs as well as cash flowing buy/holds.
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)
I find the best way to find good wholesalers is by being patient & building relationships. The best wholesalers who have the best deals only really market to the same few people. Find an ambitious up & comer & be by their side as they grow.