The eBay jobs are technically in violation of the National Electrical Code, as there is no way to insure that they are on a dedicated circuit, and also, they are not "permanently attached." If you plug one in, it probably will work to some extent. It likely voids the terms of your homeowner's insurance, if any, so if your house burns down, you could be on your own.
Another side effect is that some newer meters read only the magnitude of power going through them, not the direction. That means that you could theoretically end up getting charged for every kWh you generate, at the regular electric rates, when the electric company should be paying you.
The legal way to set things up is to contact your electric company and ask what you need to do. In our case, the electric company said that as long as a building inspector signed off, they were pretty much good with it. We got a permit from the City to install solar, which cost $200, and the inspector came by and signed off. Then the electric company came by, saw the signoff, and a few days later, sent us a formal letter with permission to connect. So we were fully covered legally.