I welcome a reputation challenge considering the amount of scamming (especially in alt-coins lately).  I provide past trades as an indicator of my trust-worthiness.  That's not to say people can't hack into a trusted member's account and start scamming.  I think John K got it right with PGP signing and I'm going to look into doing that myself.  Anyway, here are a few transactions I have to refer to:

This thread has several vouches for my XRP trades.
I also sold $1300 in GPUs here: https://bitcointalk.org/index.php?topic=184952.0
I sold $900 in BTC-e codes here: https://bitcointalk.org/index.php?topic=173675.0
I sold BTC for Paypal here: https://bitcointalk.org/index.php?topic=205472.0