The "only" problem with that, can..... be that they now have a contact, and if that person is good, they now have a good DJ, a DJ who can do kids parties CAN do adult gigs, most adult DJ's as seen here dont wanna, but if you can handle some kids, you can handle screaming drunks. It is a bit of a hard line to follow. I would only recommend a fellow DJ I already know and between us we give each others leads, I mean sometimes your double booked right. ALSO beware if you advise someone, referrals can come back and bite you on your ass. If that person is lousy, your reputation is on the line, you can "usually" know how good you are, but not a stranger.
I have also had let a DJ know about a gig and that person tried to screw my DJ friend over, so I got it in the head.
Best answer for me now, is "hi I can't do your gig because xyz, I would love to help you next time, I don't have any recommendations because I can't guarantee there work and would want you to have a problem"
When I was having severe problems, I had to turn down a wedding and she soooo wanted me, but couldn't and I was very tactful about not recommending anyone, mainly because I was new in Canada and didnt know anyone LOL, that was my excuse