Easy solution. If a ML starts getting jealous try the following;
1) Stop paying her for extra. If she says anything or seems to change her attitude then ask her what she wants from you, a bf or your money.
2) Ask for her phone number. If she won't give it to you, tell her that all your REAL friends give you theirs.
3) Ask to start seeing you outside the shop.
Item 1 is the best way to separate the girls you should avoid making jealous from those you shouldn't give a fuck about.