To be honest, I find the notion of buying limpets, or buying anything at all, in your own carrier a bit daft.
I would prefer to have storage for those kinds of things, and you could buy limpets from stations and stockpile them on the carrier for future usage.
Uhuh, that's what I mean.
At the extreme, it might mean you could stock up with limpets for free and then dispose of them for Cr100 each, thus providing an unlimited (if really, really dull) source of credits.
I suppose it could be explained as you "hiring" NPC crew to provide services aboard your Carrier (provide limpets, UniCart, commodity traders, Authority Contacts etc) and there might be some penalty (limpets cost more, you get paid less for data or CBs etc) for using them.