If done right, it's probably a good thing. But, you'll never know if it was done right until you own it a little while or tear down the engine and inspect. It's a good idea to buy a gasket set when you buy a used bike. Pull the cylinder and inspect and measure the piston, cylinder and rings and rod. Pull the side covers and see if there is any play in the crank bearings. If everything is good, put it back together and you're out $40 in gasket set. If something is bad, replace it and you're good to go. But honestly, on a two stroke, the engine is the easy part. It's the fork seals, shock, brakes, cables, sprockets, chains, bushings and etc that add up unexpectedly. Of course, you can visually inspect most of those fairly well before buying.