Let users generate their own affiliate code.

When signing up, other users (either buyers or sellers) can use that code.

If they get a buyer to sign up with it, the affiliate earns a % (say 50%) on BMS buyer fees from that buyer's purchases.

If they get seller to sign up with it, the affiliate earns a % (say 50%) of BMS seller fees from that seller's sales.

Also, when someone signs up with a referral code, if they buy parking their buyer fee is reduced 50%.

Note though, so if the buyer fee is originally $200, then the affiliate gets $50, since the fee is now $100 and they get 50% of that ($50). This data may need to be stored differently and broken more and call it buyer fee $50, affiliateBuyerCommision $50, and likewise for seller affiliates (there can be a buyer affiliate and seller affiliate for a sale).

Ideally it'd be good to indicate the discount as a line item to the buyer.

For affiliates, they should also be able to track their earnings and eventually get paid out automatically.