You will probably want at minimum the source code and some additional hours of support in case something goes wrong where the support could expire in a few mont

You will probably want at minimum the source code and some additional hours of support in case something goes wrong where the support could expire in a few months. Effectively what you need to think about is when you purchase the website, what might go wrong and what will you need to get it back and running? Once the sale is complete, if there's nothing stated in place, the seller has no obligation to fix any issues.