Something I don't own? No, but I could see this happening if I had a sterilizeable toy at my disposable from a fuck friend. If I used it enough times to write an accurate review I would have no problem writing a review on it.
Something I've never tried? NO! That is unethical and just plain wrong.
I have to agree with all of the other people who have posted before me.. Why would anyone do this? How could you even review something you have never tried? That would make me mad if I read a review and decided to purchase it based on the person's opinion of it, just to find out they didn't even know what they were talking about.! Grrrr