It is true that accounts on default trust (as well as escrow accounts) are sold, however the purchaser has incentives not to scam with them because those types of accounts tend to be very expensive. The purchaser would likely be better off over the long term of acting honestly and continuing to offer their services and collecting fees for such.
With that being said, you should also not trust excessive amounts of money with any one person to avoid giving them incentives to run away (see maidak).
I feel that the sold DT accounts/escrow accounts should have a neutral trust rating atleast on them so that people just don't assume to be trading with the same person as before. There are so many escrows here whom users deal and trust for every trade they make. If the escrow does sell his account, how can that be identified except from the pwd being changed? It doesn't make anyone trustworthy here if people who recommend using escrow only sell their accounts and leave the community.