You don't, basically. Unless you want something that will be 20% less by the end of two years.
And unless you're buying a new car, and it spends a large portion of time in the mechanic's shop, it's not a lemon.
A used car, is not a lemon.
A new car that doesn't meet the requirements, is not a lemon.
My advice, buy a cheap used car. Pay it off immediately. Don't finance, don't lease. Just make it yours, and be done with it.