I can think of quite a few situations where it works.
"So, how about this: You come here, I show you some cars, you choose the one you want and I buy it with my employee discount and you pay me back."
"Every week you come here, I show you some cars, and you tell me you don't like any of them."
This has come up in the Russian course as well - the English verb "to show" cannot stand without an indirect/dative object. In the Russian course they have the English translation of "я покажу где находится чай" rendered as "I will show where the tea is" which you simply cannot say. "I will show you/her/Pete where the tea is" etc is right. Similarly here it has to be rendered with a dative object "I show you/her/Pete some cars"
I agree that English 'show' needs an object, but I think it can be a direct (accusative) object as well as an indirect (dative) object. For example: 'He showed his cards'.
Also possible is an indirect (dative) object without a direct object: 'They think they are clever, but I showed them!'
"Showing one's cards/hand/true colours etc" is idiomatic, and doesn't follow the general rule which is that "show" has to have a dative object. In your example "'They think they are clever, but I showed them!'" there is a dative object (them) so I don't think that that invalidates my argument.