Selling parts and lack of manners.

I won't pull the trigger till I get a postage rate. I'm trying to buy a part right now that the seller wants almost twice the cost of a large flat rate USPS box? Postage can turn a good deal bad!
But if I am the first to reply to a sale ad I do expect first right of refusal. That said, I'm on here checking every day so I won't leave a seller hanging. I usually wait for a postage quote, if it is fair, I jump.