It's interesting. However, I can see people [not necessarily you] offering it for free, and then when you have a few thousand bit coins on your hand, and have spent a few hours setting it up, realize it is very tempting to take 1btc for your efforts, regardless of whether or not it was pre-agreed to.
That would defeat the whole point of escrow, which is acting as a trusted third party who will only do what is agreed upon, per the escrow contract. If I wanted 1 BTC, I would factor that into my fees. A 1.5% to 2.5% fee for escrow is reasonable.