You aren't responsible for cancelling. They pull the order, send you the total. Then you decide if you want to continue. Nothing wrong with this approach. If you don't respond and they send it, that is on them. If you decline or don't respond, back on the shelf it goes.
If something by size and weight is $20 to ship and the total to ship is double that, not cool IMO. I can box up about 10-15 kits in an hour and get labels done all manual. $5-7 a box charge would be good, cover cost, especially for having staff that does that job anyways with an integrated system. Back to the profit center approach. Being integrated where the customer enters shipping info is a huge time saver.
Want to pick at their business, start one and see how much fun it is to compute a shipping quote and not lose your *** on many of the shipments. Small companies have a tough time with shipping systems to come up with an accurate quote without significant time and expense to implement those systems. Walmart, amazon, summit get huge shipping discounts to keep their business.
They cover their ***. just like you want yours covered using this approach. Don't like it shop elsewhere. hard truth!