Here's the math, for those interested... The return gets better on multiple rolls sold due to the nature of combining shipping:
One roll -> $15.50 minus PayPal/eBay fees of 13% total ->$13.48 minus cost of standard shipping on 9oz ($3.34 USPS) -> $10.14 minus the $10.00fv of the roll leaves FOURTEEN CENTS PROFIT on one roll.
Two rolls -> $31.00 minus PayPal/eBay fees of 13% total ->$26.97 minus cost of Priority flat rate shipping in a standard flat rate box ($7.05 USPS) -> $19.92 minus the $20.00fv leaves a SEVEN CENT LOSS on two rolls.
The KEY is, once you get above selling two rolls to a single buyer you can start to squeeze more into a single small flat rate box but pay the same to ship. I would estimate you could probably fit at least ten rolls in one small flat rate box.
Ten rolls -> $155.00 minus PayPal/eBay fees of 13% total ->$134.85 minus cost of Priority flat rate shipping in a standard flat rate box ($7.05 USPS) ->$127.80 minus the $100fv invested leaves $27.80 PROFIT on ten rolls
Bottom line, for every roll over TWO that the seller sells he profits about $3.50 because of combining shipping.
Not much to say about the ethic at play other than if people are dumb enough to demand it at that price, someone is going to supply it.
You are pretty close, but using 13% to estimate fees works best for higher dollar amounts as it ignores the $0.30 paypal transaction fee which is significant for lower sales prices. I just recently started selling stuff on ebay and some of what I am selling falls into the $3-$5 range, so I just finished going through this analysis for myself to figure out if it is was worth it.
For example, if you charge a shipping cost of $1.09 and you sell an item for $0.50, the paypal and ebay fees collected will be $0.51 (or 31.7%) of the total $ collected ($1.59), but as your sales price increases, the fee % drops.
Note: The following table assumes the sale was from one of the 50 free listings a month and the shipping cost was set to $1.09 and $1.09 was your actual shipping expenses at cost (no extra $ built in).
Total sale without shipping (Fees charged - fee %) - [Amount left to acquire the item being sold] - {Net if item acquired at 50% sale price}
---------------------------------------
$0.50 ($0.51 - 31.77%) - [-$0.01] - {$0.26
loss}
$1.00 ($0.57 - 27.25%) - [$0.43] - {$0.07
loss}
$2.00 ($0.70 - 22.61%) - [$1.30] - {$0.30 profit}
$3.00 ($0.83 - 20.24%) - [$2.17] - {$0.67 profit}
$4.00 ($0.96 - 18.79%) - [$3.04] - {$1.04 profit}
$5.00 ($1.09 - 17.83%) - [$3.91] - {$1.41 profit}
$10.00 ($1.73 - 15.61%) - [$8.27] - {$3.27 profit}
$20.00 ($3.02 - 14.32%) - [$16.98] - {$6.98 profit}
$50.00 ($6.89 - 13.49%) - [$43.11] - {$18.11 profit}
$100.00 ($13.34 - 13.20%) - [$86.66] - {36.66 profit}
$500.00 ($64.94 - 12.96%) - [$435.06] - {$185.06 profit}
The high fee % for low sales prices is why it isn't worth selling low $ items on ebay. Obviously if you acquire the item for less than 50% of the final sales price, you will make more and can sell some things for $1, but you aren't making much per transaction.
Taken to an extreme, say for some reason you wanted to sell an empty envelope on ebay listed with free shipping. Your actual shipping cost today would be $0.50 for the stamp and say $0.05 for the envelope (includes the ink to address it). To break even you would need to sell that empty envelope for $0.98.
Getting back to the example, we are both assuming the seller is using a free listing or else there will also be an ebay insertion fee of approximately $0.35. We are also assuming the user does not run an ebay store or else the fee structure is different.
I reran the numbers subtracting the paypal transaction fee using your shipping costs.
Single roll:
It would be a $0.14
loss on a single roll before subtracting expenses such as the cost of the envelope, paper and ink for the packing slip, etc.
Two rolls:
It would be a $0.35
loss before subtracting actual shipping expenses.
Three rolls:
It would be a $3.15
profit before subtracting shipping expenses.
For each roll after the third:
As stated, there would be an additional $3.50
profit as there wouldn't be any additional shipping expenses.
If it were me, I wouldn't sell less than 3 rolls as it would be at a loss.