He did not respond on his possessions, but asked when he would be getting his deposit back?

  :)And there are companies here in Oregon and Wa that hook up with RE brokers , ( these companies are HML) they track all the sales have a very sophisticated software system. they bid for you and also provide the cash for you at sale.So it goes like this.say you want to bid on a 200k house you need 40k. you deposit that with them.they win the bid they put up the 200k .. they take a security interest on the recipt from auction.. then when trustee's deed comes they roll that into a HML.they charge a fee for the buy .. and then charge you for the HML usually 4 and 14 , and then you do the rehab and your free to use anyone to resell. 

When we run the credit report, it will show previous addresses and alias names; the addresses will either match up or they won't.

Should I collect a security deposit, and upfront payment even though I'm sure he did that with the previous landlord? 

I will  pass on stainless steel and keep white frig, stove, and  add matching mic  and repair other major fixes required.  

They will give you a call to discuss and answer any preliminary questions which will be helpful so you don't waste either of your's time if it's not a match, if it looks like a potential match then they will email you the two items I referenced above.

Are you holding a large deposit to keep him from leaving without notice?

If the investment return matches your objectives, than I would absolutely consider it.

Seller agreed in principal had his attorney review the P&S (same on @Justin Silverio  uses) and told him not to sign it.  2 objections the low initial deposit.. that's no big deal.  

Unless a customer maintains substantial deposits, nearly every commercial bank charges fees to customers to open checking accounts.