Most handguns will have other significant wear to the total overall gun, before the barrel is worn out..
It is a very rare thing that any handgun has enough rounds through it to the point of the barrel being "worn out".
Especially if the handgun has had diet mostly of lead bullets, it is almost impossible to wear the barrel out. Anything can be done, and I am speaking mostly of newer (30 years) handguns.
I have owned and competed with handguns that I have personaly put though in excess of 100,000rds and they still Ransom rested 2" groups at 50yds.
So to answer your question, round count is an indicator, but not the entire story.
I will never hesitate to buy a used gun, if after I inspect it, find it to be in good overall shape.
If you don't feel confident enough for a good check of the handgun, have someone you trust inspect it. There are some very good deals to be had.
But remember, it's your money and only buy something you are happy with.
