I would advise you not to leave a retaliatory feedback just for that.  If you were not on DT, it might be arguably OK but my feeling is that you have to pull back a lot when you're on DT.  I don't even look at my feedback much; I'm sure I've got negs from people I've never dealt with or even left trust for.

When I occasionally make sales threads, I usually specify in the terms that it'll be a neutral-feedback transaction so that I don't get people wanting to deal with me for a positive one.  I haven't given out a lot of green trust since I got on DT, maybe 3 or 4.  I think that's being prudent.

It's good you're asking about this.  When I got put on DT, Lauda made some very useful suggestions, but he/she doesn't seem to be around much anymore and it'd be great if she/he responded to your dilemma here.