I don't think the part people are seeing is the "sale" piece - or not everyone is.
I'd absolutely ask you to send first on a trade.
I personally might ask you to send first on a sale - but would totally understand if you didn't because I have some level of Paypal protection. Obviously my loss if you didn't send first and that'd be up to me if I was willing to lose the purchase over it.
If I were you I'd offer to use a middle man - that way you are protected as well as the buyer - and you don't have to "send first" that way on a sale.
There is another thread on here about that where a brand new person sent first on a sale - and 90% of people said he was nuts for doing it since the buyer had Paypal protection.