Never. It's their space, not mine.
I feel the same way about auto dealers that slap their names on vehicles they sell. If they want me to buy the thing and they've had the temerity to stick their name on it, they get to scrape off. Period. Not arguments, no concessions. Off it comes. It's my vehicle, not theirs.
so....... you buy a Ford, then you take off their emblem?
You get a Maytag dishwasher, and rip off their emblem?
You get a Harley Davidson cruiser and paint over their logo?
You buy a pair of Dickies pants and rip off the tag?
I actually SELL my logo to people. People pay money, for a sticker of my logo. That's... advertising.
I try to stick it small on the back of things, or like on trailers, just a small one in the corner. I always ask first though. Rarely do they say no. But I also don't put it anywhere it could be considered a "eyesore", for example... on the front of a sign.
It takes a balance...