Treat every customer's ideas as if they are lottery tickets, scratch below the surface and see if you can find a million dollars.
So a customer sends you an idea for your product. Apparently this customer wants to use the product for something that it wasn't designed to do. In fact, you don't like the idea at all.
You want to be polite and the last thing you want to do is tick off the customer by rejecting her idea. You respond; "Thank you for your idea, we will review your idea with our product development team and consider it for a future version of the product"... Knowing full well that you have no intentions of further review, much-less implementing that idea.
I hope the paragraph above is not the way you actually handle customer ideas. Not only is that the easy way of avoiding conflict, it is downright gutless and doesn't help you or the customers.
Let's consider the customer first. She was trying to tell you something about your product. Perhaps it was not meeting her needs adequately, or maybe she really likes your product and would like to expand it's use. At some point she is going to wonder; "what ever happened to my idea?". What if she asks you that question after a few months? Are you going to make up another lie? "I submitted your idea to our product development team, but no decision as been made yet.." , blah, blah, blah... Who is in charge here anyway? You are losing credibility. Can't get anything done. Can't even get a status update on a simple suggestion.
From your company's perspective, maybe you should dig a little deeper. Even with bad ideas. If you just ask, "Why is that important?", you might be able to reveal an underlying problem with your product that all customers are suffering from. Or better yet, you might find that there is a whole new market for your product. Sometimes the original idea leads you to a better understanding of customer needs, and then you find an inexpensive solution that this priceless in value to the customers. Treat your pool of ideas as if there is a "million dollar idea" hidden in the stack, you just have to find it. There could be more than one; its kind-of like lottery tickets, the more you have, the better your chances of winning.
Treat every customers' ideas as if they are lottery tickets, scratch below the surface and see if you can find a million dollars. Whatever you do, don't just throw them away!