and use various escrows who are in the default trust network for the sole purpose of getting a trusted trust feedback (they may not always trade with themselves, however escrows on DT who give trust after every trade appear to be highly sought after).
This pisses me off to no end. There is no reason to give positive feedback to people you escrowed a deal for. Nothing is displayed that warrants that, the escrow does not actually risk anything - if someone doesn't send, they just return the goods/BTC of the person who did send. There is pretty much no reason for the escrow to be giving positive rep. Unfortunately, this happens a lot and you see lots of inflated trust scores with people who have 0-BTC risked trust all over the place.
I personally will very rarely leave positive trust when I escrow and when I do, it will be after a number of smooth deals that are large in size and I am confident that the person I am leaving trust for is not trying to farm trust; but even then I will generally not proactively leave trust (they will need to ask).
I have discussed this issue with a number of other escrows and I will generally give the same opinion as yours. The viewpoint that is usually given to me is that there should be a record of a successful trade, although I have noticed that some of these escrows have started leaving neutral instead of positive ratings.
The new trust algo has made it more difficult to farm trust this way because only the first trust rating you get from someone will count towards your trust score. Previously getting 4 trust ratings from an escrow in the default trust network would mean the calculation would factor in all 4 ratings.
There are valid situations for escrow leaving a positive feedback. Eg:- if the trade had a big amount or if the trade took a long time and if there was good involvement from buyer/seller, then leaving a feedback is good. But leaving feedback for each and every trades escrowed or each and every trades done is not at all a good idea especially if the user is in default trust list. See
https://bitcointalk.org/index.php?action=trust;u=223869, for example. TBZ should not leave feedback like that IMHO.
If TBZ did work upfront then received payment after the fact then he risked not receiving payment and this is the definition of when trust should be left (even though they are for small amounts). Generally speaking, if you risk money with someone in a trade then you should certainly leave a trust rating.