Keyboards with legs

I sold a new keyboard to a customer yesterday morning and he went off quite happily with it. Half an hour later, the phone rang. It was my customer:
Hello. I've just set my keyboard up with my computer but it's wobbling. I can't get it level at all.

It should have 2 little legs at the back which you pull out so that it stays level.

No, I've looked. There's nothing like that. I'll have to bring it back. Wait a minute. I'll just go upstairs and have another look.

(I wait on the phone for the next few minutes.)

Hello? Yes, actually there are two legs to pull out. I didn't see them before. It' fine now.

All in a day's work. Remember my idea about passing a test before being allowed to have a computer? Seems like a good idea. :)