One question is whether the author wrote all the software or used any pre-existing GPLed software. If the person on the web site owns the copyright completely, then the web site may impose any conditions, including those incompatible with the GPL. Of course, releasing it under the GPL gives you some rights by itself. In particular, you can't redistribute without the source code, but you can make copies and use them.
The above practice is generally considered unfriendly by Free and Open Source Software advocates. Since it's not really honest to advertise GPLv2 and not deliver everything necessary, I'd advise being careful about the product. People who deliberately misrepresent things in advertising are likely to be selling shoddy software.
If the software contains pre-existing GPLed components, and the author didn't come to other terms with the copyright holders, then the GPL applies in full. The distributor has to provide source code (either with the executable or on request at nominal cost) and may not impose restrictions not allowed by the GPL.
There's also the possibility that the author released under GPLv2 without actually understanding the license. This happens from time to time, and frequently the FSF will quietly work with companies on getting into compliance.
In either case, it's perfectly fine to sell the software. If somebody else has the software including the source, they can redistribute freely, and it's perfectly legal for you to get it from them.