I disagree with everyone here, while you shouldn’t recommend to the “highest bidder” at all, there is nothing wrong with obtaining a small “finders fee” from the people you are recommending.
The way my group of contacts does it, the person “receiving” the job offers money to the person who “finds” it, depending on the pay rate and term of employment. This really works well with fellow freelancers as situations are often reversed.
If you, or other people, are not comfortable asking for / offering money, you can also make sure to recommend each other, pass each others’ work around, or even just buy lunch.
Of course, you should never recommend someone for a position unless you think they’re the best for the job. More important than fees, or work, is your reputation.