The word
clever and
sales are synonymous with a used car dealer in my mind. No thank you. I don't pretend to speak for others, but I do think that the old "add 3.75%" to the existing asking price accomplishes nothing. It goes like this:
Buyer: I want to buy your knife.
Seller: I'm asking $435 + $7.95 for shipping, $6 extra for insurance, and add the 3.75% and the original 30¢. Or we can do $435, net to me, or you can use "gift"...

Buyer: can you possibly just give me a single price, don't make me sit here and do math that is apparently too complicated for you to do. This isn't math class. I'm trying to give you money.
Seller: $old!/Withdrawn for now, thx BF!
Buyer: WTF??
Go through that enough times it gets irritating. Maybe some people love the thrill of the general mathematics, other people are busy, see something that want, but the seller insists on setting obstacles. For what purpose? As far as the gasoline example, they can write 10/9 if they want to, when I fill my vehicles with fuel, i know what the fixed price per gallon is. End of story.
Gift removes the buyers protection, because there is an assumption that the money is, well....a friggin gift. That knife I'm buying ain't a gift, it's $435 and a whole lot of other extra fluff added on. Where is the gift? Will it be a gift when paypal locks your account for evading the policy and ToS and you cannot refund someone because their money is tied up to be damned in your account? Problems man, I don't know about you but i like to try and avoid them myself.