It is revolving credit, so if they just need money to finance AR, it is very cheap indeed (0%). They can alternate cards each month to double the amount of 0% money- provided they are just using it for AR.
If they need the money to finance operations, then their model is wrong. Never borrow against a credit card for operations, only for AR because of the crazy interest. Otherwise, you end up without sales and large debt. Ask mom and dad, grandma, you uncle, friends if the goal is not not give up equity but you need cash for a longer term investment in the company.
Keep in mind, 50% of marriages fail and they have sex, so don't think it is easy or even natural.