If you escrow on someplace like localbitcoins.com only you can cancel the order.
You could do a balance check (I'm assuming this functionality exists) with time showing, and keep that to submit to the localbitcoins resolution staff in case they need to make a determination to resolve the escrow.
Other than that, pick the most reputable user and look carefully for negative feedback. Somebody with hundreds of positive transactions isn't likely to reverse that trend on you.