Every broke two stroke ever sold "just needs a piston mate"
If it really just needs a "piston" they are saying it is down on compression as the rings are no longer sealing to the bore, if that was true then they are implying they wouldn't just fit rings, but a whole piston because they like to do it properly...or more likely they can't just spend the £5 on a set of rings, reuse the old gaskets and flog it running...because there is more wrong or they aint got a clue - and if they aint got a clue I wouldn't buy a 2 stroke off them as they are pretty highly strung things and if not preventatively maintained can need a lot of money spending sorting them when they break..