People are motivated by money, plain and simple. I would say money and recognition. Recognition is great but ultimately pats on the back get old when money doesn't come with it.
I've worked in sales for a number of organizations and nothing makes me more annoyed and dis-incentivized as knowing I'm making my company or my boss a fortune and I'm getting nothing or getting peanuts in return.
If you're making money be generous with your sales people, it will keep them motivated to keep making you money. When organizations start to give stickers, promotions in name only, pats on the back and aren't giving anything concrete it takes away all incentive for sales people to perform.