The profit on this higher amount using a 25% seller's margin would be something like (using the higher $20 amount) $20 x 0.25 = $5. The tax on this $5 would be something like $5 x 0.15 = $0.75 in tax "contribution" from the underground economy due to embedded taxes (or perhaps $3.75 optimistically in the buyer's favor in viewing the whole transaction) instead of $100 x 0.23 = $23.00 under the FairTax.
Using your own math and those same numbers from your example above please show where the seller gets the $23.00 for the fairtax and what he would have left after remitting it....
On the $100 sale, the FairTax would be $23.00. The seller would keep none of that since he is paid to collect it and send it to the state. You can't understand $100 x 0.23 = $23.00???
Could you subtract $23.00 from $100.00 to see what the seller had left???