I've done hundreds of DSD's and plenty of 'Try Dives' as well. Without blowing my own trumpet too hard, it's rare for someone to dislike the experience.
That said, I actively discourage some guests from doing it if I feel they lack the basic water skills or comfort level required for a successful dive.
Depth is usually the 'killer' and leads to more and more negative experiences with DSD's. I rarely go below 4m during mine, but then I'm blessed with shallow tropical reefs here in the Maldives. In certain locations where the reefs were a bit deeper then stress levels for everyone involved increased exponentially, ears become problematic etc.
Something that I've noticed during my years as a 'pro' is that the longer I'm diving, the shallower I'm guiding and teaching. After a thousand hours underwater, diving simply isn't new or exciting anymore. Don't get me wrong- I really like diving and teaching... but I believe this is required for a good instructor. OTOH you get the arrogant, boaster-type who brag about maximum depths, air consumption, weight required, how fast they can teach etc. They are generally 'bad' teachers because they're still diving for themselves and get frustrated at 'only' diving to 2.5ata.
I rarely have someone who intended only on doing a DSD commit to a course immediately after. Normally in my typical locations, a DSD dive is on a 'things to do while on vacation' list. However more than a few students who do sign up for a course have already tried diving a couple of years back... so while it may not be with me, I like to think that some people end up taking a full course later on.