I'd save up a bit more and get a new one. I took the chance and got a good one but I know a few others haven't, if I had to get another one I wouldn't take the chance.
it was a good easy mod 4 - 5 years ago and you could get nearly new turbos for 200 quid everywhereeven the latest used k03s turbos will be from a car 6/7 years old now, and in my opinion that's a gamble