You can always expect people to act out of their own best interests. Do they get paid a commision? Maybe they have a stake in the company, if the company sells more, then they make money. Or maybe, if they don't approach you their boss will yell at them. Take your pick.
I'd suggest, you just say, "Thank you, but I can find it on my own." And let it go. Don't get worked up over it, and try to see their point of view.