We never "make" money on shipping, because we always charge what we pay (or less) plus $3 for packing materials.
I have sometimes considered using flimsier, lighter weight tubes and boxes, but I would be trading one problem (people who complain the shipping is "too high") for another (lots of damaged packages and tubes).
We also will send via any method the buyer wants (if it is more than our flat rate price, they must pay the difference).
We always quote all USPS and UPS options (we don't quote FED EX or DHL, but if the buyer wants, we would send those ways).