recommendations on a good used cd player for under $750

I would be very reluctant to buy used especially when for your buget Marantz has two players that are very good the cd5005 (399) and the cd6005 (499 comes with USB input on front for your iphone). Both sound very good. I've bought some used cd players but you never really know how much life is left in them. Some have been ok but some didn't last too long.

It's a risk buying used but you'll likely get much more of a player over a new one at the  same price; plus the new player is worth about half once you crack the box.

Marantz, NAD, and Cambridge players are all very good in that range new. If you have a nice system but not the most revealing, no doubt you'll be very happy with a new player from about any manufacture in your budget. Not sure anyone really makes a bad player today unless you buy it at Walmart.

If you're looking for a great used player and don't need Blu-ray or SACD the Cambridge 840c is a player to consider. On a system that can reveal the differences between components the 840c is going to pull ahead of the new players in the same price range. 

Marantz and and the others are really good players, but you'll almost always get more buying used. If you're wanting to stay closer to $300 then definitely agree on a newer Marantz. 

I would try the Emotiva erc-3. I have heard nothing but good reviews about it ($499).