Your photo doesn't show how the heel plate of the blade is sitting on the heel of the boot. Assuming it's sitting flush, that's a substantial gap between the sole plate of the blade and the sole of the boot. I personally wouldn't attempt to pull the sole of the boot that much via mounting screws.
Other considerations:
(1) What boot do you have?
(2) At this point all we can conclude is that there is a substantial mismatch between the blade and boot. Which can be caused by (a) defective boot, (b) defective blade, (c) defective boot and defective blade, or (d) boot and blade are both OK, but they are just not suitable mates (there are considerable variations in mounting geometries between different boot and blade manufacturers). You will need further investigation to check this out.
(3) As a practical matter, what do you plan to do if others write in and agree with the seller? The tech you're dealing with won't take the risk of mounting the blades, so you'll need to shop around for a tech who will.
(4) If you end up stuck with the boots and blades that you have, a safer mounting alternative would be to insert a shim to fill in the gap. But that may throw off the pitch of the boot too much, and you may need to adjust the mount at the heel as well to correct (and causing some change in overall height). And you won't know until you try it to see whether you're OK with it.. This is a matter of last resort if there are no returns (boot or blade or both).