Looks very unfair to them. The C$ on your side equals about a target dog/light leopard tier, so we are valuing the C$ there.
Cake dogs: 12 mid-advents together (Rarity wise, excluding poor demand)
Palomino Tess horse: About 5 mid-advents (Rarity wise, excluding poor demand
C$: About 2 mid-advents worth (Valuing at Target dog/light leopard)
Ice rat: About 8 mid-advents
Light Heart rat: 5 mid-advents
+About 5 2009 rares worth, and if added to the extra rare in the target dog, makes about 1 mid-advent.
Rarity wise, your side equals about 33 mid-advents, which is a little less than what a non-balloon is worth (A non-balloon is 8 tiers under the ur foal). I would probably take it considering most of your pets have poor demand and it is decent overpay. I'd recommend getting a second opinion, just to be sure.