Liberty Reserve (LR) is non-reversible, just as Bitcoins and (for the most part) MoneyPak codes are.
With LR and MoneyPak there isn't much opportunity for escrow to be done, without there being fees and risks to the escrow partner.
Do you have a trust rating on the #bitcoin-otc Web of Trust (WoT) perhaps so that a trader can be more comfortable entering this type of trade? (or, will you send the MoneyPak first if the trader has a good trust history with the WoT?)
Incidentally there is a BTC -> MoneyPak service, http://BTCPak.com but they don't work with LR so this might be a useful service for some.
I can however provide you with LR, Western Union, and Virtual Credit Cards.
So you are saying that you will also accept a MoneyPak code and will then pay out Liberty Reserve (or Western Union, or Virtual Credit Cards) for those MoneyPak funds?