Thank you for your quick response. Another thing I am not sure about is either using flat rate boxes, or regular priority boxes.
I also plan on selling the stuff from my grandmothers house. She was a HUGE antiques collector, I mean HUGE. With two of her own shops in the back. And since she passed away, we need to clean out the house and the barns because my grandfather will be moving in with us. But this won't be for a while because I want to get my feet wet with little things first, like purfume bottles, etc.
There is so much for me to learn, I guess it's going to be a trial and error type thing.
So it would be safe for me to input the weight, dimensions of the box on USPS and just use my zip code (I live in NY) and a destination zip code for somewhere like California, to try and determine a shipping cost estimate that way.
I am sorry for asking so many questions, I just want to do everything right, and try to get a good reputation and to be fair.
I feel like a deer in headlights right now, LOL.