Which guide do you use?
If you don't use any guides at all and trade by year and rarity: all trades are overpay on the other side.
Trade 1: the brown dog is a very rare from christmas 2008 (same event as your pet) so they would be a fair swap.
Trade 2: the other side is worth 1 2008VR + 1 2010 rare (valuing each 2019 store pet at 1 2010R)
Trade 3: they're offering 5 very rares from 2008 and more add so it would be some major overpay on the other side.
If you use the rarity guide: The angel advent turned VR on August 2010. There isn't a set value to fill the gaps so it's up to you to decide what fills the date gaps
Trade 1: the purple star bobtail turned VR on March 2011, in my opinion 1 2011 rare would be more than enough to fill this gap since it's pretty small.
Trade 2: The white sortic turned VR on January 2019. In my opinion this would be about fair since the gap is quite large.
Trade 3: the card dogs turned VR on January 2019, the mini husky turned VR on June 2011, the candycane bwolf turned VR on March 2011, the tan october moon turned VR on March 2013,
the black dutch bun and the store pet have been VR since release so it's a massive overpay on the other side. the other person was probably using the rares list to make this offer, it would be nice to let them know that you don't use it!