You cannot sell an Amazon seller account. The seller account is either attached to you or it is attached to the business.

What you can do which kind of gets a bit messy is transfer your account to another business entity or another person and this could be part of a sale of a business.

There is therefore really no value to the actual business account but there is value to your business.

Look at this way, could you sell your bank account? If so how much would you sell it for? You then realise that the value of the bank account is not the account itself.

If you transfer an account, Amazon will recognise that the person or people behind the account are different. If you have someone who has been banned from selling on Amzon for say breaching policy etc, they couldn't just go and buy another Amazon account in good standing.

If you want to sell a fully fledged business with an Amazon marketplace attached to it this is slightly different than just selling an Amazon account. If you have a business that is purely an Amazon account, I'm not sure whether this would be a viable proposition for anyone to buy or to sell. The problem being is that Amazon hold all the cards and would not be obliged to the same terms on an incoming party.

This is another reason why Amazon push on the branding as it is very easy with far more protection selling a brand than selling an account. If you sold branded goods on Amazon and decided one day that you wanted to sell, you would get the buyer to set up their own Amazon account and then get them to sell your branded goods and then sell them the brand.