pssst...George Clooney sent me, wanna read my novel?
You mentioned you have a different process for selecting new clients when you are given a referral. Can you elaborate on that? And how does Miss Snark feel about her clients referring other writers to her? Does it change your opinion of a client if they recommend someone whose writing Miss Snark decides is total crapola?
There are two kinds of referrals from clients. One is real; the other -for lack of a better phrase - is pass the buck.
The first one is when clients, or authors I know, or editors, (or even other agents sometimes) send me someone and say "this author is worth considering". Well, I may be Snarkly but I'm not shortsighted. I read the manuscript. All of it. Right then. Average turnaround time is less than a week and it's often overnight. When someone does you the service of sending you a prospect, you don't sit around in your sarong and write odes to Grecian Formula One racecar drivers.
The second category come "from clients" but the client doesn't mention it . I get query letters that begin "I met Amy Author at her reading at Kepler's and she said to query you". Yea right. The correct translation is you asked who her agent was and she told you. Those aren't referrals, those are query letters with some research. These are handled just like all the other query letters but with a more personal rejection.
The difference is that I take it seriously when someone I trust has READ your work and thinks I'd like it, and do well by the author.
Does it matter if a client sends me crap? Nope. If it happened a lot, maybe, but so far so good. Clients are not eager to make their agent reluctant to talk to them for any reason, let alone for considering some other schmuck's work!