Preliminary warning: before posting this question, I searched this site's corresponding section (warcraftpets.c o m/downloads/pet_addons) (*), I went to the search menu here (warcraftpets.c o m/community/forum/search.php?keywords=auction+house&fid[0]=2) which is a bit tedious to browse, and I google'd also and the only thing I found is this now unavailable "plugin" (thebuddyforum.c o m/honorbuddy-forum/plugins/uncataloged/102730-plugin-battle-pet-auction-viewer.html) someone created a year ago. - but which seems to do exactly what I want:
I just would like a way to filter the "Battle Pets" menu of the Auction House, to only display pets I don't have. I currently have to hover my mouse on all auctions, and try to locate the ones where the "collected : X/3" line doesn't appear. Not very handy..
There is apparently no way to do that ingame, so I'll have to look in add-ons.
I am quite a big fan of "light" add-ons, which do exactly what I want : I love BattlePetBreedID or Rematch, because the first is not invasive (a small window added at the most, and a few characters for the breed behind Battle Pets references ingame) and the second one has an independent small window easy to manipulate.
I have read here and there that Pet Tracker or Pokemon Trainer might have has this feature, but these are "all-in-one" addons with lots of features I don't need, so it is far from my favorite option ...
Is there any light add-on doing this? I would be surprised it hasn't been created yet .. (I would gladly do it if I had the skills to create an add-on

(*) Sorry for unformatted links: forum won't let me post them as I am a new poster..