Yes you can.
Use different browsers, or else use private browsing, which is CTRL + SHIFT + N on Chrome. Then of course, use different e-mail addresses and passwords.
As a buyer, you can have multiple accounts without any problems, however as a seller, you'll have to jump through a few hoops. However, with a little legwork it's quite possible. Keep in mind that as a seller, you'll have to supply them your social number, sometimes toward the end of the year. However, TIN will suffice. (taxpayer identification number). It starts with 9 and has the same number of digits as your social. I don't think though that they match a social number to a name; they probably want to make sure that no other seller is using the same.
Want to have multiple Seller Accounts? Use your brother's, sister's, etc. Ladies can change their last name to their maiden name. Then a new address (trusted friend), a new credit card, bank account and voila! A new TIN (see above).
Make sure you NEVER post on their Forums. You'd be forced to post under your Seller Name, thus being vulnerable to the bullies that are plenty of. They'd put you out of business by purchasing your products and then giving you negs (negative feedback), and you're toast. There is a site that is unrelated to Amazon; it comes in Google search as Seller Soapbox index. This one is safe, and you are NOT required to register under your Seller name.
Hope this helps.