hi, i am about to get a wheelset, and found a good deal of deep V (28 spokes F&R) on CL, but just wondering if it's possible to determine whether a wheel has been trued or not? and even it's trued, will this affect its performance in a long run? btw, i am 220 lbs...

When you mount it spin it at a slow speed by hand and watch how it passes your brake pad. If it doesn't wobble back and forth or up and down then it's true and needs no attention. If you notice some side to side variation or the edge of the rim going up and down as it passes the pad then some time on the truing stand is likely a good investment.

Then test the dish of the wheel. Measure in from the seat tube or fork leg to the braking surface. If they are the same to within 1 mm then you're fine. If they are up to 2 mm out then I'd live with it. Once it hits 2mm it's time to have the wheel trued up.

thanks!
but is it possible to see whether the wheel's trued before or not? coz i am going to get one from craigslist.

I think I know what you mean .. are you asking, "can I tell whether the wheel has previously gone out of true, and then been retrued?"

I don't know. But if the wheels run true just now, and the spoke tension is even all around on each side, then I think the wheel must be OK. I'd be interested in comments from more experienced wheel builders.

That's right. Consistent and adequate tension are the most critical things for longevity but I don't see how the OP can know this before hand unless he just asks- and trusts the seller.

Actually no. Often new wheels are out-of-true and may have uneven spoke tension.

theoretically any wheel would go through a truing process when it is built. new wheels can come out of true soon after building from riding / vibration. i would assume that these wheels are fine, unless otherwise stated.

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.