Check them out to be sure they are round. I bought a wheel from a member, and it was out-of-round, cost a few bucks to get it fixed.Just take them to a garage, and mount it on the machine they use to speed balance - turn it slowly by hand and it will be immediately evident if they are out.
check with the sanctioning body as to whether they'll pass scrutineering/inspection at your track sessions.
... use a piece of strong hardwood( oak or hickory) to act as a "drift" betwen hammer and rim. This eliminates any chance of a missed blow and also marring the rim too badly. You could even profile the end of the wood to match the curvature of the rim.Take a hammer and pound it back into place.