Well buying a china girl engine is iffy at best. No matter where you buy you might luck out and get a really good engine, then again you might get an engine that keeps breaking down. Remember the engines are made in china, no matter who sells it it's still made in china.
What you want is a new engine, made recently, not one that was made many years ago and sitting on a shelf or boat somewhere. And you ask, well how do I know which are which? And there's the tricky part. Most sellers won't tell you how old their engine is. But there are things to look for. For instance you want an engine with 8mm cylinder bolts not 6mm. Look for an engine with upgrades such as heat shields on the exhaust and chromed so it will last. The newer builds have speed carburetors. What I did myself was buy an engine from BikeBerry then bought the exact same engine on Ebay. The Ebay engine was $70 less.
First engine purchased.
Second engine purchased.
On the second url scroll down to see the engine kit. It's no longer available from this seller but it gives clues for what to look for. Also the kit I received did not have that carburetor, it came with a speed carb. But both engines are Power King engines. It was much cheaper, free shipping, no tax and oh not painted.
If I was going to buy a third engine today, this is the one I'd buy. It fits all my criteria.
Hope this helps, remember when you buy off anyone other than a dealer there are risks involved. Question you have to ask yourself do you feel lucky? Well do you punk? lololol Just kidding! I feel good about the last one.