(tough|tricky|awkward) customer
Plural
tough customers
1
someone who is difficult to please or deal with, and is often demanding or critical in their expectations
- He’s a tough customer when negotiating prices.
- The waiter handled the tricky customer with patience.
- She’s an awkward customer who always finds something to complain about.
- The mechanic dealt with a tough customer who refused to pay.
- His reputation as a tricky customer made people cautious around him.