I am seeing this, too. The Squarespace UPS quotes are 2 x higher than the actual postage rate for UPS.
UPS postage that I buy for a 40lb box from NY to UT for example: $55.52
Squarespace "quote" from UPS and charge to my customer if I have that kind of shipping set up for the same size and weight package is $120. It's too high.
A possible work around would be applying a negative % markup to get the prices more where they should be. But you can't put in a negative number there.
Anyone have other solutions aside from manually assigning postage rates for every zip code?