I don’t mind having things presented to me.
If I am not interested, I don’t answer.
Letters that obviously came from someone who took the time to look at the site are usually read, blind mails that are obvious cookie cutter products go mostly in the trash and after that mail from that sender is usually just ignored.
I do keep a folder where I keep mails from places that got a “maybe later” in my mind, and when space opens up, I do look at that folder.
We also have to keep in mind that we are a group of people with very different cultural backgrounds. Some cultures for instance consider “haggling” a normal part of daily life, others take or leave an offer and are done with it. What can be considered “friendly” in one culture, is “intrusion into privacy” elsewhere. What may be “polite and proper” in one place is “cold” in another. And so on and so on.
So if you say “no” but also point out some things about the program, it may be considered an invitation to negotiate by the other party.
Of course this is assuming that some personal contact has been made.
Indiscriminate mailings are still spam. I hate reading “I have come across your website and find it very interesting” and then the mail goes on to sell something (link exchanges, aff programs etc). If you have actually been to my website, I think you have something more to say about it. Don’t lie with the first sentence (or any other).
If someone obviously has looked the site over, and writes about a concrete offer presenting facts, even if I am not interested and don’t reply now, I may get back to it at a later date.