I take credit cards (as Prime Time Freeware).  It costs me something like
$0.60 per transaction plus 3% of the purchase price.  If you need the
exact numbers, let me know and I'll dig them up.

I think you could get around the "factoring" question by offering the
services of several firms under one roof.  As long as you receive the
money and then pay your "sub-contractors", it should be OK.  (You would
be retailing the services, in effect).