See https://prodesigntools.com/dont-buy-adobe-software-on-ebay-craigslist-or-amazon-marketplace.html
It is easy enough to download the software from the Adobe website and install it as a 30 day trial version.
After 30 days, the software will no longer run until a valid serial number is entered.
The problem with buying a serial number online is that you have no idea if it's a valid serial number which will be accepted by the Adobe activation servers until you actually type it in on your own computer and press Enter.
Doesn't matter how many assurances you get from the vendor. If it doesn't work, it doesn't work and is probably pirated. Then you have to chase your money back from the vendor which is highly unlikely.
Note also that true transfers of valid serial numbers also require a Transfer of License form to be completed by both vendor and buyer and then processed by Adobe so that the serial number is linked to your Adobe ID.
Transfer an Adobe product license