Gabriel ~

I would pay the commission if they did the work. 

You really need to look at your long term reputation in the Recruiting / Staffing industry. Reputations are built on how other perceive and interrupt your actions. Reputations are not on facts or the long nasty story of he said she said.  If you get a reputation of "stealing commission" good luck get top talent to work in your shop.  Plus, no matter how you present it to your current staff they will always be leery so that if and when they leave it will never be a smooth transition for you or them.

Couple of facts:

• Every change to your business whether it hiring or firing someone it effects your GM’s by a minimum 10%
• Depending on how you handle it that 10% can be a negative or positive.
• It cost an agency on average 75k (45k base + 10K in training + 10K on boarding + 10K interviewing time) to hire a recruiter.
• The first year a recruiter is in your shop you might break even.
• The second and third year they should be making you money.

The long and the short ~ take the high road and pay them. 

We have ALL been there and trust me when I say, Your ego will recover :-)