Don't let clients put on their own condom.
You put it on, holding the teet so you know it's on properly.
Do not let the man handle his penis at all when the condom is on.
No matter how awkward it is trying to reach you should have your hand on his cock frequently in any position just to make sure condom is still on. You guide the cock inside, not him.
Then broken condoms can happen, but will be VERY rare.
Use a bit of lube and apply it to the end of his dick once the condom is on - something like liquid silk - NO OIL.
There are some bastards who deliberately break condoms and they are very practised at it.