Again, Vernor v Autodesk (2010) will say otherwise. In that instance, Vernor was buying off ebay to resell. He didn't even load it on to his computer (AutoCAD), however, it was determined that due to the license that the original buyers had, they didn't have the ability to sell their copy to Vernor, thus he didn't have the ability to re sell it.
Buy extension, you buy from ebay from someone that doesn't have the ability to legally sell the software, you don't really own it, thus no rights associated with ownership.
This is the same protection that we all use. We do, with our designs, our proofs, for those that make fonts, they do with their fonts. I do with my stock embroidery designs that I sell or the embroidery fonts that I digitize for a specific program.
You have to read the contract. Rather you do or do not, you use the software, you are bound to the contract. Especially considering that very court ruling listed above and to my knowledge that is the latest law on this particular subject. Unless the contract is deemed non binding in your jurisdiction. In that particular court ruling, it was stated that the owners can pretty much write what ever type of EULA that they wanted it it would be considered binding. Vernor tried to get it re-heard, he was denied by the district court that ruled in AutoDesk's favor and denied by the Supreme Court. Unless there is another decision to change that, that is still good law. Rather you like it or not.
Don't confuse what you may or may not be able to get away with, with what is legal or not.