I have bought many pictures of Istock photo in the past. I stopped buying at home once they were acquired by Getty.
I've always bought in digital format and usually the smallest image available. The main reason I did this was that I used the images on websites and that I did not need a higher resolution image for that.
All the other artwork / photos I own were purchased in person in a physical place where I flipped through a bunch of photos (like in an art exhibit, a craft show or in the gift shop of a historical site). I do not remember ever buying posters, wall art or anything like that online. It's not that I'm against doing it. This is simply due to the fact that I never have the itch to go shopping online for wall art. These are always impulsive purchases made at a place where I browse various collections and where something catches my eye.