You should sign the address that has these BTC. I'm not interested but trying to help you.. most will dismiss this thread thinking you're trying to con them into sending first. There has been a increase in these members the past week or so.
That being said, watch out for scammers wanting you to send first.
Here no middleman service? , i've been scammed out of 0.47 btc because of paypal chargesback
Neteller and skrill can also be charged back and someone sending first to you won't prevent a charge back, neither would using escrow.
I still recommend escrow.
Nobody should send first to you even if the payment is reversible.Can you sign the address that holds the coins you are selling?