Then you're breaking the law. Even moreso than P@P file-sharers, in fact, since you are actually making a profit on the physical product created and distributed by the record company, rather than an abstract form of the data within the product.
You're not alone, of course: there are thousands of used CD stores in the US, and every one of them is reselling a copyrighted product without the express consent of the copyright owner. Yet the RIAA isn't filing mass lawsuits against the owners of your local Second Spin.
If I didn't know any better, I'd think the RIAA was suing schoolkids and grandparents because it's easier than making a valid case, both legally and in the court of public opinion, subject to counterpoints and scrutiny. Much easier to scare a kid's mother into paying $2000 than going to court against a legitimate business and proving that the CD would have brought them $2000 had it not been resold.
RIAA is essentially a trust, the same as the steel trust or the biscuit trust etc. that existed and were broken up at the turn of the century. They control (through their member parties) the vast majority of music released to the public (at least that above the level of garage bands) and have engaged in price-fixing and collusion to keep the price of music artificially high, while forcing artists to submit their work at artificially low prices. We still do have anti-trust laws in this country, and I'm surprised that some enterprising young district attorney hasn't filed criminal charges.
Consider the case of another trust: DeBeer's (the diamond trust). They control the vast majority of new diamonds on the market, and they deliberately conspire to keep the price of diamonds artificially high. The diamond trust is well aware that what they're doing is illegal in the US, so much so that DeBeer's corporate executives are forbidden to as much as change planes in the US, lest they get served with a summons. All their US advertising is farmed out to advertising companies here and handled remotely.