Surely if you can tell that the pros could too and if they could they would never make a failed challenge on a shot they hit - but they do don't they?
I've never seen a pro challenge a call that was 3 inches or more off, except Safin at Wimby. I've also never seen an official be more than 3 inches off too. 3 inches inside the line and 3 inches out is easy to "feel". It's the area in between that you cant "feel".
I think opponents who think they can tell if their ball will be 3 inches out the moment it leaves their racquet are a problem. You see it out, you call it out, they think you have cheated them because the moment it left their racquet they thought it was in.
If I "feel" like I hit my ball 3 inches long and my opponent calls it long, why would I complain?
The only time I question a line call is if I hit it, it feels good off the racket, and it looks like it was inside the line when it lands. That's the point where I get a bit skeptical. If I hit a ball, it feels "close", it looks like it hit the line, but they call it out, I dont really complain. I know through experience that balls I see "on the line" can definitely be out.
And partners too. One of my doubles partners thinks he can always tell if his serve is in. When an opponent calls it out straight away, no hesitation, and his partner agrees I want to move on to the next point but my partner wants to start an argument. It is painful, it puts me off my game. Last week on one serve I thought the opposition were correct to say out, but they were so nice that when my partner acted nasty the guy just gave us the point! It was awful.
The last time I challenged someone on a line call was when it was absolutely obvious they were not making good calls. The final straw was the player calling a ball "out" when it looked like it was a FOOT inside the baseline. I actually said "WHAT??! No... no... no... that's like the 3rd one already". Set score was 4-2 in the first set. On the change over my partner asked me what we should do and I told her that if it happens one more time we have to call lines people because it's impossible to play like this. It turns out, after I said that, his partner started correcting his calls. It ended pretty peacefully.
Out of 1000's of sets, i've only had to complain about line calls once, and only twice has someone said something about my line calls. When I say "complain" I mean "coming to the net" or worse (involving an official, or getting captains, ect.). Everyone has those 1-2 *roll eyes* moments per match, but it's usually not worse than that.
I honestly think men's 4.0 and 4.5 has the worst line calls from hooking, but I've seen some of the 3.5ish women make the worst in terms of slow balls that are 6"+ in (usually about 6" inside the line) and they call it out.
Unintentional bad line calls seem to happen much more at the lower levels because they arnt even looking at the ball when it lands, cant read spin, ect. Intentionally bad line calls seem to happen at the same frequency regardless of level.