Since "BUDGET" was a consideration for this thread-
There are a lot of used bikes out there that, although they may not be considered "high quality", are totally fine, serviceable bikes.
Bikes that are still much better than xmart type bikes.
The main thing is that it'll function well without having to stick a lot of additional cash into it.
Many of the nicer things like alloy wheels etc. are good to have, but not totally necessary for a casual rider.
Probably one of the best things to do is be patient and ready to "pounce" when you do see that "super deal" on CL.