I am an alumni interviewere…I get a nice percentage of my kids getting admitted but not many attending.
How do you “sell” your school?
I have been a parent volunteer interviewer at D09’s school. It’s across the country from us, so kids typically want to know that there will be some familiar things there. We talk about the eco-focus, organic student-run farm, recycling, and decent coffee a lot – living here in the Pacific NW, those things are important! Other than that, it’s mostly about listening to what’s important to them, and highlighting things about the school that address their needs.
When my D was still in school, we often tag-teamed – I’d do the official interview, and after that was complete, she would come over to answer questions (I’d leave). Worked great!
Honestly, though, kids apply to so many schools, you can’t feel badly when they don’t pick yours. Even when you know it’s the best choice! 
Yes I’m an alumni interviewer for Duke. Honestly though I’m lucky if one out of 10 students that I interview gets accepted.
But for the ones that get accepted I follow up with a phone call and personalized email.
I did interviews for about 3 years for my Ivy. But I stopped after every year, the one kid I DIDN’T connect with (I am being nice) was the only one admitted
I think you need to know to what schools you’re losing admitted students. I’m in a state with a FANTASTIC public – a “reach” school for many kids throughout the country. Every top kid who applies to my college has applied to this school via Early Action. Kids who apply to my school also are applying to other pgms where full ride merit scholarships are in the picture. We lose kids mostly to full rides to the top public school, other full ride merits and also, to “top ten USNWR” schools in general (H, S, P, M).
These are the main two categories of kids turning down my Ivy. All we can do is humanize our college experience and cross our fingers. 2 years ago, I was speaking to the family of a fantastic admitted kid, valedictorian in my daughter’s nationally super-high ranked HS. My college’s very generous fin aid offer simply couldn’t match the buckets of $ the big-name public school was giving his family. It was prom night and parents were dropping off kids for photos at a scenic location. The next day was the final matriculation decision. My school was the kid’s top choice and I was talking to the dad to have him speak to fin aid. Didn’t work out. Kid logically turned us down for the in-state school. It happens.
I have been an alum interviewer for my undergrad. I think the applicants connect with the younger alums.
I did it for a few years for my undergraduate school. Although I’m not a young’un per @jym626’s point, I think I have an interesting career path and set of professional activities. I explained in part how what I do benefitted from attending my alma mater. However, I don’t think the alumni report on the interview receives any attention in the process. And, in those years the probability of admission dropped to under 7%, I think. As a result, over several years, I don’t think any of my interviewees were admitted (though many looked reasonably strong). I’m not one to spend my time on useless activities, so I stopped.
i was an alum interviewer for Harvard for 10+ years. I had three admits and loved them all. Two enrolled, and I lost the third to Yale. Miserable.
Selling is about showing your love for your school. Don’t hold back.