Shock! Americans aren't rude

I've been selling beads (and before that jewellery) for quite a while on Etsy and have lots of lovely customers in the USA. In fact, today I have realised that I have even more lovely American customers than I realised.

I get quite a few requests for custom beads and a fairly typical one liner is:
"Could I get more of these"

If I were writing that to someone, I would add a please on the end.

I was brought up with manners being important. Very. Not saying please or thank got a more severe telling off than running through the house with dirty shoes on (or setting fire to a saucepan ... or encouraging my sister to put a motorised spinning top in her hair ... but those are stories for another day).

Anyway, I'm not one (normally) to turn down business so I would (usually) reply in a jovial and friendly manner, get a good two-way conversation going, find out the customer is actually pretty nice and wonder why on earth they were so rude and bossy in their original message. This has happened upteen times so when I got another this morning, I put an irritated complaint into Google
"Americans don't say please"

and Google duly obliged with a link to this enlightening article

Such a good job I did because it turns out "could" seems to be the American polite word when asking a small favour. Adding please is overkill, too formal and might be interpreted as bossy. I'm appalled with myself for not checking this out sooner.

To any American who caught me on a bad day and so received short shrift and got an unhelpful answer, I must go through my messages and apologise most humbly. Could you forgive me, please? I know, I know. I'm also sorry I added the "please" but I can't help it, I'm British (and my mum would tell me off!)

Do you have any examples where cultural differences have led to misunderstandings?