FSS Seller = A seller that GovDeals is handling payment processing for.  For example, we're allowing the customer to make payment via credit card, PayPal and/or Wire Transfer via Liquidity, and then we're paying the seller on the back-end of the transaction.

Non-FSS Seller = A seller that is solely handling payment.  For example, the customer cannot make payment via credit card or PayPal.  The seller expects the buyer to either pay them at the time of pick-up, or the seller has instructions on where to wire/send payment to their personal bank account/address.

To identify whether a seller is FSS or Non-FSS, you can see via the "Financial" box within the LEAP seller record.  Alternatively, you can go to a buyer record, then click "winning bids," and then there will be an asterisk next to the seller's name if it is a FSS seller.