Sometimes I think I should start a Pinterest board for the Tender Trap. But there are so many examples, I wouldn't have time for much else. So I'll stick to just posting some especially outrageous examples once in a while.
What I call the tender trap is a deliberate error. A lot of people who aren't familiar with toy trains place the tender backwards because they think it looks better. If it was as simple as that, I wouldn't say anything -- but in order for them to place the tender backwards, they have to deliberately ignore how the train's hooked together.
For example: here's one I found on eBay.
Look closely at the couplers. The engine has a bent pin. On the far end of the tender is a tab -- designed to hold the bent pin. But the seller chose to reverse the tender, forcing the pin into the knuckle coupler.
Notice something else -- the back of the tender has a blank wall. So how was the coal supposed to get from it to the engine cab? Here's the way it's supposed to look.
And here's another view.
Personally, I think having the correct end of the tender connected to the engine "looks right." And all you have to do is just match up the links. How hard is that?