I don't know why someone would would want a grommet in each corner.... it's not like they're gonna put a bungee in each corner and stretch it out. The Cor-X simply won't tolerate that kinda pull. If they want to screw it fast to something, why not just got through the Cor-X with a screw and washer ??
Anyway, if someone order 10 signs and then come back and asked for grommets in it, I'd say why, they won't dangle like that. They aren't strong enough, but if you want to add to your order, that'll be an additional $45.00, please.
On another note, we just finished 460 30" x 30" 2-sided Cor-X signs for a customer.
However, up front, I asked them how they were to be used and they said they would hang from the ceilings.
I then asked how ?? Rope ?? Chain ?? Wire, cable.... what ??
Wire.
Do you want grommets in them ??
Yeah, Okay.
Now............. you can figure it into the price.
You need to get these things straightened out up front. Being blindsided by customers always looks bad if you charge them for something that appears to be trivial. I know it's about principle, but it's human nature.... and even more so these days.