I think there are several things a vendor can do if they do not have bloom photos, especially if the plant up for auction is a hybrid. If the plant is a species, you can always suggest that the bidder use an internet search engine to locate photos of that species. If it is a hybrid - it may be too new for photos to exist, but there are other things a seller can do.
Even without a flower photo, displaying a photo of the actual plant up for auction gives the bidder a chance to see exactly what condition the plant is in, what size it is, the color of the leaves, the number of growths, the size in relation to its pot - all of these things are important to a buyer. For example, a plant might be advertised in a 5" pot, but the photo might reveal that it really belongs in a 3" pot.
In the case of hybrids, sometimes all you can expect is a good photo of each parent if the auction plant has not yet bloomed. Sometimes a photo is available of a previously-bloomed sibling from the same cross.
If a photo is available but permission to use it cannot be acquired, then the next best thing is to carefully describe the flower using those writing skills you insisted to your 7th grade Creative Writing instructor that you would never need.
I have used all of these methods to sell unbloomed seedlings for hundreds of dollars - and never had to resort to stealing someone else's photo. You never really get a second chance to clear your name once the Net starts talkin' smack about you so you just can't ever give it a chance to start.
There's just no excuse to steal photos. The disgusting sense of entitlement many people feel just because there isn't a lock and key on something is nauseating. It's not only stealing, it demonstrates a complete lack of respect for anyone else, and it could be a sad prediction of how your transaction will go - with the vendor showing that same lack of respect and consideration for you.
