If the Chinese engine is a copy of a Briggs, it will probably have a zinc flywheel key, as the Briggs does. This is done deliberately so that if you hit a solid object with the blade, and the crankshaft stops suddenly, the flywheel key will shear and protect the crankshaft from torsional failure. If the mower has hit something massive, the key will be sheared, and because the ignition timing is set by the flywheel, not the piston, it will still have a nice spark, it just won't happen when the piston is at the top of the stroke. If that has happened, compression will be normal but the mower will not start. To check, you have to expose the flywheel by removing the top cover. Then remove the flywheel retaining nut and look closely at the key. You should be able to see if the keyway in the crankshaft is out of line with the keyway in the flywheel. If that has happened you have to remove the flywheel and fit a new key.
If the key is OK, it will be necessary to go through a standard diagnostic process - we can help you with that. First though, I suggest you follow Bruce's advice and check the key. He has an uncanny knack of going straight to the problem.
If the key is sheared, the problem is not Chinese quality, it is your mate's treatment of the mower. It is possible to have it happen the very first time you use a really nice mower - all you have to do is try really hard to mow a water pipe.
