What do you think?

I think it's a pretty poor thing to do. If you don't have a camera, say so and use a manufacturer's picture, identifying it as such. If the product is unopened, then do the same thing. If a person wants to use another person's picture, he could have the courtesy to ask.

And here's another point, what if somebody thinks your picture is the one lifted from the other person and thinks you're the one who is being deceitful? I'd like this practice to be discouraged by the forum administrators when pointed out to them, unless it's a manufacturer's photo.

On a related point, I had an ad not too long ago. A few days after the ad expired, there was a new listing for the same product. I had a look at it out of curiosity. The guy used his own pictures but he cut and pasted my description of the product! I didn't know what to think. On the one hand I thought it was flattering he liked my description. On the other hand, you feel like the person is somewhat underhanded. It makes you wonder what else the person would do. Certainly not anyone I would trust to deal with.

I understand the feeling of having one's territory invaded. But as territorial I am, I can't see any real harm. I wouldn't do that but then I have a camera. In a case where someone does not have a camera, maybe he needs to sell his item to obtain one. All just one man's opinion, of course.

Given the circumstances (unopened box) it seems pretty harmless to me but of course who knows what is actually in the box? He should have definitely said something like "since mine is unopened, here is someone else's pix of the same item", or used manufacturer's image.

I think he should have e-mailed the original ad picture owner, (in this case Muzikat) and told him what he was doing and asked permission to use the picture.

Legally speaking, once you put it on the internet, it becomes public property (ask these idiot movie stars caught emailing nude photos).
Ethically, the seller should have made sure that this was footnoted clearly as a "sample" picture. Should he/she ask your permission? Why? You don't own the photo any more, there is no representation of the photo pertaining to you personally and you are not being misrepresented in any manner.
It's not like he broke into your hard drive and stole the photo?
If it bugs you so much, learn how to use photoshop and put a watermark on all of your photos.