As far as wholesaling or bird-dogging, you go where the investors want to buy. You would need to create a buyer's list of investor, what areas they are looking at and know how to put together a wholesale package. Merely sending an investor an address and price just won't cut it with an experienced investor. In the wholesale package you will need to include the ARV, cost of repairs and price it according to MAO.
If you are looking at buying, rehabbing and flipping, this can be done in any area where houses are selling. And right now, that is just about everywhere except the "war zones". In Detroit specifically, some of the great areas are East English Village, Cork Town, Indian Village. But most of Detroit is selling. You just need to have someone who knows the area really well, can provide you with great comps and give you good advice about which areas to stay away from.
Hope this helps.
Kathy Persha, Assoc. Broker/Realtor/Investor
GRI, CDPE, SFR, CIAS