"Would you go into a bank wearing your helmet?"
No, I wouldn't. And I wouldn't go to a petrol station to arrange a mortgage.
I'm buying petrol FFS, me walking in to pay with a lid on shouldn't be a big deal.
Some of us do find having to take the helmet off a massive nuisance.
I wear spectacles and ride in all weathers. When it's raining I can fill the tank and pay without getting my hands wet if I leave the helmet on. If I take it off, I have to take my specs off first and there's the problem of not having anywhere to put either item where they're not going to slip or get blown to the ground. By the time I've finished paying and have dried specs and hands (assuming the garage has any paper towels left in the dispenser) the process has taken twice as long as it normally does.
If you're unencumbered by the need to wear glasses, a fair weather rider and are happy to acquiesce to their ridiculous demands, then go ahead. But I don't accept that we should be perceived as criminals for wearing a helmet, nor do I accept that my choice of helmets should be limited to flip-front ones at the whim of Shell/BP etc.
It's not as if helmet rules like this are going to have any effect on crime. All the stations I use on my regular route have ANPR cameras, so attempting to ride off without paying isn't going to work more than once. It's not about that anyway... walking into the shop with the helmet on that is what they're objecting to.
I do sympathise with staff who've been subjected to threats and attacks by thugs intent on robbing the place, but making innocent motorcyclists show their faces isn't going to alter the habits of criminals unless the rule is enforced by a couple of bouncers at the door. This is all about management wanting to be seen to be doing something to calm the fears of the till operators. In fact it'll achieve nothing other than setting up confrontational situations for the staff and driving a few, admittedly unprofitable, customers away.
At least when my local Sainsbury's tried this policy I was able to suggest they'd lose not only my fuel purchases for bike and car, but my weekly groceries shopping as well. Allowing helmeted customers to pay for fuel at the night-pay window (i.e. no need for me to enter the shop) had been a constructive alternative I gave them, but after a few weeks they abandoned the policy completely.