The usual answer is whatever you're willing to pay. However, I believe that doing your research is key. Is the language used to describe the turntable a tad over the top? Does it say things like: "Technics is the greatest maker of turntables.....responsible for the Techincs SP-10?MKii.....so therefore aiming to gloss over the fact that the Technics SLJ110R they are selling is pretty awful but still encouraging you to buy the dream. Don't fall for it - Google/YouTube/Audiokarma/Vinylengine etc is your friend.
Of course you may be tempted to overpay for a turntable that isn't too bad simply because the one you're aiming to buy has fancy new feet, or has had some custom veneer added to the plastic sides. Sure - if that works for you then buy away but a few things to remember:
- the new fancy feet probably aren't doing the same job the previous original feet were doing (it's important)
- that custom veneer might look great but if you ever try to resell your turntable, it won't fetch a great price because it's no longer original
I try to ensure that whatever I sell is described accurately. I don't sell any donkeys. Each turntable is fully serviced, fully functional and I have also listened to it extensively. And each of them sounds great at that price point.