https://www.ebay.co.uk/itm/Microsof...503665?hash=item3fe25a3a71:g:6zwAAOSwOWpe0Ecb
I don't think you should get this one.
"- Came with Dell PC and is new.
- I don't have a licence key for it.
- All working so no returns"
"All working" means he has to install it to know that. "Came with Dell PC" also means he has installed it and that it is an OEM disk. An OEM disk is from a specific computer manufacturer (in this case Dell) and they are loaded with extra junk, mostly unwanted, sometimes difficult to get rid of. "No license key" is because he has already used the license key to use this OS on his Dell computer.
https://www.ebay.co.uk/itm/Window-XP-64-bit/293754615049?hash=item446523b509:g:SF4AAOSwKFlfbxCD
This says "Like new" which is not the same as "New". Almost certainly a "Used" one. Also 64 bit is not generally recommended. I have never used the 64 bit but I have heard that it causes many problems. 32 bit is the most widely used and trouble free XP version.
https://www.ebay.co.uk/itm/Genuine-...908417?hash=item23e17ccf01:g:d08AAOSw1wtfcPhC
This seller is another crook on ebay. Zoom the picture and look at the left hand edge where it says in red letters "For distribution only with a new PC" The writing at the top left mentions OEM twice. Below that you can see "Licensed for distribution only to specific countries in Europe"
Go for one where the seller says some thing like "Unopened", "in original sealed package" with "product key" which is essential to register your product. Otherwise Microsoft will block you off after one month. Another idea is to buy from a seller in the country you live in which should make 'returns' easier. Ebay is full of crooks like this. You need to be very careful. I have seen far more genuine stuff on Amazon. I suggest you look around there.
If you get an XP with SP 2 don't forget to add SP 3 after installation and fully update the set up afterwards, all the way to 2020. You can get help here for both these tasks.