How can you tell if a bun has ear mites

I had my friends lop bunny here for five weeks, and it turns out he has ear mites. I'm concerned that he may have caught it from mine, although I have no idea how to tell if they have them!

I've checked their ears and they are perfectly clean.. I was trying bond him with a foster bun and her ears are very clean also. :?

While chip was here he didn't itch his ears once, so I had no idea that he had them, and it makes me wonder how you actually can tell if they have them!

With ear mites the bun will usually be scratching and shaking her head, and there is normally some dark crusty wax present: the vet can check this under the microscope for mites