IDEA: Do not wait to fire lousy sales reps; this is the reason you should always hire more sales personnel than you think you need.

Do not wait; terminate lousy salespeople within a short time period. If you know they are not going to succeed, do not waste the money; let them go so you can focus on the successful ones and start looking for replacements. This is another reason you should always hire more sales reps than you think you need.  Half will not work out, let them go and start looking for more even though you have your customers covered for now.  Another reason for getting rid of them quickly is that if you do not, you are likely to take your time hiring their replacement (poor reaction but common).

You would not have these problems if you always hire great candidates but that is the problem. You need to hire more than you need because of all the employees you have, the most important are the sales reps.  Start looking for more great candidates.  What is the worst that happens?  They sell too much?  Most companies and sales managers would like to have that problem.