Stylish Ten "you come here before, we have $20 minimum on credit card". New York, New York

 
February 25,12  I got my nails done at Stylish Ten, when I went to pay the full amount of $ 9.50 using my debit card with Visa logo. One of the owners name Xixi said that the minimum on credit card is $ 20. I told her that that minimum is ridiculously high. She proceeded shouting at me saying "you know I have minimum.... you come before."

I said "please lower your voice first, second I never come here to get just manicure, maybe that's why I never experience this inconvinience. If is legal what you are doing, I recommend you to have it in written by the credit card company, not by hand." 

She proceeded to tell me to take out money from the ATM, which charges me $ 2 to withdraw money. I asked if I could include the manicurist gratuity of $5. And it would be $15.50. She said no, pointing at another hand-written paper on the wall that says" please tip in cash." I did not say anything else, because it was useless to argue with her.

Does the Credit Cards comany set this hight minimum amount for business services? 
And if business owner claim they have to pay for the cause of processing the charges, what is the legal percentage to be charge? 
 And how can gratuity be also asked to giving in cash?

Would you please help me?

"Thank you for your time."