abctoo is wrong. He is trying to make the case that
ebay would keep track of millions of independent T&Cs which is simply stupid.
ebay has one set of T&Cs although it is true that they allow some flexibility for terms such as returns but sellers have to abide by the return choices within the 'My
ebay' form. Here is the
ebay returns policy; note it says nothing about 'just write your own return policy'; instead it implicitly says "You agree to comply with
our returns policy."

Sellers are required to handle returns within the return options supplied by the My
ebay' listing form.
ebay makes the rules,
ebay enforces their rules; they do not enforce other people's rules. Why would
ebay be willing to try to interpret and then enforce millions of listings each with their own set of Terms and Conditions? It makes absolutely no sense.
The fact that clueless sellers often write additional return T&Cs in their listings is simply a sign that
ebay is not willing to try to police stupidity.
abctoo, folks are welcome to post opinions but please do not post misinformation. Consider the kind of headaches you could be generating if anyone tried to follow your incorrect interpretation. You are not posting an opinion about a stamp or cover, you are posting incorrect misinformation that could lead others to make costly mistakes.
Don