Shipping rates on site always lower


First time poster, apologies if I'm made any errors here.

I've bought a decent bit, only an occasional seller. One challenge I find on the site is that the calculated shipping rates are so far off from what Fedex/UPS actually charge me. (typically charged almost 50% more, so nearly $300 when the site says $200). There are no additional charges that explain this, as I've had both shippers break down the costs of things like insurance etc. I've experimented with a host of local shipping places in the big city I live in, and honestly YES the different locations do seem to charge me different, and categorize things differently. But all are still way, way beyond this magical number Audiogon comes up with -- like $200 for shipping speakers. Ha!

Am I missing something? I don't need to be told to do a workaround, I need to know what the formula is I'm supposed to use in that workaround. Honestly buyers are very adamant -- if I try to tell them shipping will be more and offer them a flat rate $20 higher to cover even a % of this discrepancy, they act like I'm an 1800s medicine show, trying to pull a fast one on them. I'm just trying to only lose a small amount of money on shipping.

Any insight, beyond the obvious?
marjon
I think that the pandemic has made shipping estimates and service guarantees all the more difficult.  Maybe things can get back to something close to normal in the months to come.
Other than Audiogon.....if your using 3rd party shipping services like THE UPS STORE....they can charge you whatever they want. They are NOT connected to UPS at all...or the actual UPS rates.
Whenever possible actually go to a UPS or FEDEX store (FEDEX OFFICE) that is owned by the actual company. Also sign up for a Business Account to save an additional %. Think I save 12% thru FEDEX on Domestic packages and up to 80% off on Foreign Packages using their Smart Rate program (Which you can only get by calling a 1-800 number that is not affiliated with their stores)
I suggest opening an account with FedEx and/or UPS, which will net you a discount. FedEx’s discount for a non-business account is listed at eight percent, but I received a fifteen percent discount after I shipped a pair of speakers and an amplifier during the same week. (Business account requires that you have a state tax number.) Once you have an account, beware features of the website that promise to save you time in getting your shipment ready to go, since those shortcuts sometimes don’t display the less expensive rate options that are available to you. 
I have a FEDEX Business account....I dont have a State Tax Number nor have I ever living in the current state I am in.  Just for your info.