I recall a joke in the 70's [George Carlin I think might have said this] - 'Jehovah's Witnesses come to town for there religious conventions with the 10 Commandments in one hand and a 10 dollar bill in the other - and they don't break either one.'
We had a 'sister' in our hall who would calculate to the very penny how much tip was proper for her food. If she had a cookie and a coffee and it came to $2.37, she would turn over the place-mat and multiply 2.37 x .15 and leave precisely 35 cents. Not a half dollar, or a dollar which is pretty common - but just precisely 15%. That might not seem bad, except that she would, like most Jw's drink plenty of coffee, demand excellent service, and always choose very inexpensive items from the menu.
I think in general they deserve a poor reputation in this area from what I have seen.
Jeff