This is simple... Start printing out your postage from the USPS site, through PayPal, or some other online electronic Postage system and have you packages ready to mail when you take them to the PO. Not only does this save you time (and money) but most likely you will never get another nasty look or attitude.
I hate walking into the PO Office now and having to wait behind an eBay seller that expects the PO Clerk to weigh and post every single package for them. It is too simple and cost effective now do it yourself right at home. Including insuring the packages now right from home with electronic postage at any time of the day you choose.
You can go right now on eBay and buy cases of 2 labels per 8.5" x 11" sheet regular type printer labels dirt cheap.
All my postage and shipping labels have been printed out from home ever since electronic postage was offered online a couple years ago. All I have to do is drop the packages off at the PO, no waiting in line. (my time is money to me)
Isn't it great! I sold some items a couple of years ago, then stopped selling until about 3 months ago. It has changed for the better. Before, even though I had paid online at the USPS website with a credit card, I still had to wait in line because the slots at the post office were not large enough to pass a box through. So I had to stand in line JUST to hand someone a box. Or to buy insurance, since they wouldn't let you buy insurance on the website. Now they've got it all set up. Only once since I started selling again has there been a need to stand in line, because the insurance limit through the website (I think $200?) wasn't enough -- the item sold for $250. But when a bidder wants to pay you that much for something, they are worth standing in line for.
That's fine for people who run eBay as a business out of their homes, who can afford the postal scales and the fees for online stamps, but what about the occasional eBay seller? Shouldn't they be treated with courtesy by an overpaid quasi-government worker?