Best used TT for under $1k?

The mk7 is not made in Japan. It is made in Malaysia. 

Rega RP-6.

How long is a piece of string?

It's ultimately an unanswerable question - far too many variables.

Assuming he hasn't yet found one:

That said, I'd suggest staying with a brand that has been around a long time continuously, has a proven record of servicing and supporting their gear, and that is reasonably widely available.  

If he wants something that's basically "turn-key," a Rega is the first that comes to mind.  Excellent reliability, excellent sound, easy to use, etc.  If he wants to noodle with it more, a used VPI could be a good choice, although there are a LOT of possible variations.  

There was a Sonogragh with arm and cart on US Audiomart over the weekend for $880.
Sonogragh, a division of CJ and made by SOTA

There is no such thing as the best used at under $1000.
There are many, as suggested.
I would recommend Denon DP75. It sells at around $1000, mostly from Japan.
https://www.ebay.com/itm/154475447440?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=533...