I was virtually "forced" into choosing the GM 24-70 over the Tamron 28-75 by market forces. Last year I was looking to completely divest myself of my Oly m4/3 Pro lenses. They represented a significant investment for me and I had a great many of them. No matter how I tried I could not sell them privately. Wex and
MPB offered me derisory amounts and I finally went into the Jessops branch where I began my Sony journey.
The Tamron was there of course and so was the GM. If I chose to go down the Tamron route then the amounts offered in P/ex were only slightly better than I had been offered. If I went the GM route then a magic wonderland of opportunity suddenly opened up in front of me.
The basic amounts offered for my m4/3 lenses suddenly became stratospheric and there was suddenly a managers special offered to me but the clincher was a 10% p/ex bonus that suddenly appeared that very instant I walked in the door.
I felt I was choking with so much gold being stuffed into my mouth, in the end the GM was only a matter of a few hundred pounds extra so I walked out into the high street with a glorious extra 4mm in focal length at the wide end and a red badge.
I still don't understand retail economics like that to this day.