How do your feel when salespersons knock at your door at odd times trying to sell something you are not interested in? I feel pity for these people who have to toil from house to house facing rejection at most of places. And yet they wear a forced smile as they start their rehearsed sales speech. When they come to me at most inconvenient time (for me) and insist on selling when I do not want to talk to them, I find it, if you will pardon me, irritating; although I do my best not to show it as I turn them away as politely as I can. Websites which have only sales pitch as their main content are very much like these salespersons who arrive when you are not looking for them. Visitors go web browsing primarily looking for specific information and not sales offer. When a visitor arrives at a website which offers information she finds useful and solutions to her problems, she is likely to visit again.
A website should not be designed only for selling something, though that may be purpose for setting up website in first place. The website should provide information and commentaries which can pre-sell product to visitor. It should attract targeted visitors interested in content. Pre-selling arouses interest in product prompting visitor to visit again. She will try to satisfy herself with information provided, testimonials, bio of webmaster, links to related sites and other considerations before she will actually buy product. In a way, pre-selling tries to guide her in this direction and makes it easier for her to make a decision.
People are more inclined to buy what they "want" instead of what they "need". Once they set their minds on buying something, they look for reasons (or call it excuses) why they should buy, only to satisfy themselves, though decision for purchase has already been taken. Pre-selling provides reasons which they find "compelling" enough to part with money.