I don't know about the present but in the past Jim Carter charged actual shipping charges, which are hard to calculate until the package is ready to ship. I prefer that to so much for a $10, so much for a $50 order, etc., no matter size and weight.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.