Ok, I pre ordered Guacamelee One Two Punch on Switch for $37.49. I also ordered Sonic Team Racing on Switch for $29.99.
After 30% off discount and 5% off red card, my total was $59.09 (after tax).
It says I received a total of $11.92 in discounts, which makes sense (30% of 29.99 = $9 + 5% of $58.48 = $2.92).
Sonic has now shipped and I canceled the Guacamelee pre order. Now it says my order total is $26.26 after tax.
Sonic was $29.99 - $5.30 (discount) + $1.57 (tax).
If you figure I got the 5% off for my red card, that would amount to a $1.50 discount.
Which means I got $3.80 in additional discount for doing the pre order and cancel trick.
Not the greatest deal, only amounting to 12.7% off in addition to the red card savings. Still, not bad if you don't have GCU.