I need some help deciding if I am going to buy this Miata. Is a vibrating shift mean something is wrong? and also does having the synchro replaced mean that he could of messed up the manual transmission?

 

It could be as simple as busted motor mounts. Then again, it could be something way worse. You could take it to a shop and have them give it a good inspection, but even then you are buying a USED vehicle. The term "Buyer Be Ware" is never more true than when buying a used car. It comes down to whether or not you are willing to take that risk.