Background: I have ADD. I've had it most of my life. It has become more pronounced since LK was born as the coping techniques I developed over the years don't really work anymore.
I was in a situation earlier this week visiting with some friends and acquaintances. The subject of ADD came up (one of the women there has a child with ADD). I brought up that I also have ADD and am working with the dr to find a therapy that will work and we've moved on to trying to find the right medication. It's a trial and error process and a little frustrating. I gave some of my experience on how ADD tends to affect you - how you process information and how it affects your decision making and daily activities, etc.
A little later when we were standing around, one acquaintance started talking to me about this product she uses that helps her memory and concentration.
Having had numerous people try and sell me on this natural cure and that one for migraines, etc, I naturally tend towards skepticism over this sort of thing. I think it probably showed on my face. I said that I have tried natural things, but now is the time for a stronger course of action that I am working out with my doctor, but please send me the info by email so I can look it over. I did not want to be completely dismissive, but the strength of her "this is the most amazing product ever" line made me feel like it was probably a direct-sell thing that she sells herself.
I got an email from her later apologizing if she was "too forward", but again extolling the virtues of this product. She didn't email me the info, and once again, I got the direct sell vibe. I sent her a message back saying that I wasn't offended by the suggestion (I wasn't) and explained where my hesitation comes from (so many friends/acquaintances who sell "miracle products" that don't really work, one acquaintance who has a product that he swears is a cure for cancer that "big pharmacy conspiracy" is keeping from the public, etc). I told her that I would be happy to check it out if it was something I could get in a health food store, but that I am not interested in direct buy remedies at this time.
My exact phrasing in the email was: "
I do believe in natural remedies and healthy eating as a solution to many health problems. However, I am seeing a nutritionist right now, as well as my family dr. I am not interested in trying anything that is a direct-buy product as a treatment plan. But if this is something I can get at a healthfood store, let me know. 
"
She emailed me back all gung-ho about this product with the link to her personal sales site. Sure enough, it's direct buy. How do I politely reply? She's nice otherwise, but I am pretty sure I made it pretty clear that I am not interested in direct buy cures. I would be happy to take a supplement that I can buy on my own terms without someone bugging me to buy more and more and more or without a big cash commitment. Otherwise, this is something I am happy to discuss with people (I do find that being open about my experience is helpful to others going through the same thing with children or other friends/family), but I am also happily working on it with my physician.