This seems to work for red mounts and may work beyond

1. If you meet mid-level horse dealer after you commission regular horse dealer, don’t sell the mount that you get from regular dealer already, reduce the commission cool-down to zero with gold and then commission the mid-level dealer.
2. If there is no senior horse dealer after you commission the mid-level dealer, repeat step 1.
3. If you meet senior dealer after you commission mid-level dealer, don’t sell the mount that you get from mid-level dealer, reduce the commission cool-down to zero with gold and then commission the senior dealer.
4. Once you meet superior dealer, you can get one fragment of red mount from him. But don’t waste your drachs on commission him, you can wait till the free daily commission.

If you fail to meet mid-level dealer at Step 1 all the time, you can give it another try in 10 minutes. Generally speaking, you will get one fragment with 100k drachs. The key is to reduce the cool-down to zero the minute a higher level dealer comes up. If you want to save some gold, you can wait 10 minutes till the cool-down is over and then commission the higher level dealer.

1st go and as soon as I go mid dealer I got the superior dealer straight away (may just be luck but worth ago - let us know how it goes if you do try)

full details at http://gamenerdblog.com/2011/03/02/bathe...ssion-strategy/