You mean like before you actually buy it? Not unless you take along your bike when you go to meet the seller and mount the wheels for a quick spin and eyeball check. All you can do is rely on the honesty of the seller.

I know that it's costly to take them in and have them trued. If you have a less important set of wheels I'd suggest you practice on them. Or find an old set of junk wheels at the local bike dumpster and just use those for practicing to get the hang of how to true up your own wheels.