Honestly, I can't even see someone's foot-fault unless it's completely obvious. Besides, I'm not even looking at the server's feet...I'm watching for contact point to split-step. Foot-faults are something I don't even think about. Now the line call cheesers.......that's a different story. That stuff infuriates me. I played a guy a couple of weeks ago that did this, and I finally had to say something the third time when I hit a screamer that was square on the line. I will not call a ball out (long/wide) unless I can clearly see that it has not caught the line, and you all know, that's not easy to do when you are trying to set up for a return or whatnot. But the last thing I want to do is be known as a cheater. I just refuse to be one. In another recent match, I reached for a ball that ended up being about four inches deep on the baseline, but I wasn't sure that it hit the ground before it hit my racquet. I immediately conceded the point.
Winning is almost everything, but honor is everything. This is a gentle(wo)man's sport.