With a smaller volume than you are handling, then it's a simpler matyter of spending 5 minutes to determine if the service is even remotely relevant. If not, a polite "No thanks" as I hang up pretty much does the trick. Otherwise, I let the poor sapsend me some colour brochures. Odds are, there will be some turn-over at that company, and I won't hear back from them for at least 18 months.
However, you (and/or your admin) talk about handling half dozen per day! At that point, or for anytime I these calls when I'm WAY TOO BUSY, I interrupt the call right near the beginning. Sometimes you know that the service is irrelevant. Just politely tell them so, and hang up (nicely). If there;s the slightest possibility that what they are suggesting has anything to do with what you do, then invite them to EMAIL their info. I like that, as it confuses, and in my mind weeds out, a lot of suspect suppliers. I figure if they can't send me the info by email (either a nicely formatted email, PDF file, or at least some decent links to their website) then I likely don't want much to do with them.
Maybe in your specific case, FAX or SNAIL mail is more appropriate to your decision making process.
I also resist all attempts at providing too much information. Again, a polite "well, gotta run" and nicely hang up.
If they get too pushy, well I push back, and all that politeness mentioned before, well it gets toned down a notch. Or two.