Well I've bitten the bullet and listed all three of my items with
MPB for part exchange rather than advertise on here.
A7Riii body
A7ii body
Sigma 135mm f1.8 ART
I chose an A9 that was listed as "excellent" rather than "as new" and my final payment was £43
.
MPB were about £90 better than Wex in the p/ex probably because they have so many A9's to shift. Wex in the past have upped a p/ex rating on a piece of my equipment when they found it to be of a higher rating, I wonder if MPB will do the same.
I almost entered my 100-400GM as a swap for a 200-600 but after looking at a few reviews I decided that the MFD of the 100-400 would suit me better in insect/dragonfly photography.