Early return charges can apply with any rental company. I remember encountering it with Budget in Boston years ago. They will argue it's loss of income since they didn't schedule that car to be available. True or not, you can bank on such a charge, but you need to phone the company and ask what the charge would be. If it's just $15 total, that seems pretty cheap. Be sure to check to see if returning it on a specific day, before another full week in the rental period is up, it doesn't subject you to a daily rate for the last few days.And, as noted, if you don't fulfill the obligations of the rental contract, your rate could skyrocket. Phone the company right away and find out what the charges would be.