So I've been stringing for a friend for a while and he always breaks string every few days. He used to use a 115 Wilson Hammer and now a steam 105S, always give him 16g or 17g. Very fast swing speed and likes to brush hard. Keeps blaming me for his strings breaking every few days and he tried using babolat pro hurricane at 16g, broke that in 3 days. Never paid me for a single string job yet. Should I completely drop him from my stringing list? What are your experiences with these kinds of people? All broken on sweetspot, notching.