Having said that, if it's an arrangement worked out with the VC beforehand, then it could possibly work.
If we're talking about acquisition rather than investment, then that's an entirely different matter of course.
Typical rates of compensation for the middle man or company run from 1% to 8% -- it depends on the deal you strike with the company looking to raise money.
Of course, you need a contract laying out your cut. And... you need to be aware that you open yourself up to being sued down the road by the investor if his investment goes south and he loses money. This happens a lot -- especially when it's a private investor and not a company investing the money. For this you'd need Professional Indemnity insurance, and you'd need it for the next 10-20 years - the lifetime of the deal, basically.
To add, the introduction itself is a very small part of the process of closing funding.
Typically consultants/bankers who help with larger fundraising rounds and charge for it would provide much more services beyond a simple introduction/recommendation.