"What's Your Best Price?"

I think Kotta gave the best answer to this question so far. Lots of ways to respond to people asking what your "best price" is: I'd suggest just telling them your best price--or saying that you'll consider reasonable offers.

I agree w/ Tvad. The response to 'obo' should be an offer, not a 'what'll you take?' request.
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I agree with Tvad. these questions don't usually come from serious buyers. Further, my best price, until I receive an offer to consider, is the one I post in the ad. Isn't that sort of implied? I recall one time however when the correspondence I had with an interested party before he asked "the question" had me comfortable he was sincere and ready to buy. I responded with a slight discount from my asking price and sold the item to him. Net is I think you can tell from the tone of the request whther it deserves a direct reply. The only inquiries I ignore are the ones that go like this:

hey - i'll give you $nn right now you pay shipping to my home

. . . where nn is a ridiculous number below my asking price.

It's a harmless question that takes all of five second to produce a response for. If you didn't want dumb questions asked, you shouldn't have posted an ad, let alone one with "obo".

Don't get me wrong. I can get irritated myself too. But, for the most part I can usually tell when items for sale will move quickly or take a little longer. It's these items that take longer that I would most likely pose the question...

Which brings me to my next point. In every instance that I've bought an item, I always ask one question in the very beginning to start the communication flowing. Most times it's: "Is this still available?" I almost always know the answer, but again, it's just to open the lines of communication.

Take it with a grain of salt. If you can't, I suspect you won't be selling too much on this site.