My business often partners with charities in sponsoring event. In exchange for them inviting their members to the event, we give them a percentage of the sales generated. My question is, what is the difference to us of treating the payment as a commission vs a charitable contribution?

I see no reason why you can't treat the donated portion of sales made at the events as a charitable contribution.

There is no real difference to the bottom line, but I would treat it as a commission paid for bookkeeping and tax purposes.