How about posting a link to the online photo, telling your potential customers that it is a link to an official manufacturer image of their product, not your particular item for sale?
That still won't cut it.
Generally, the instant the shutter clicks the copyright to the photo is owned by the photographer (to make it clear, that's the person holding the camera or who put it on a tripod, and no one else) unless it is there is a contract for "work for hire" which most pros are loathe to sign off on anyway.
How enforceable is that copyright? Well, if the guy is a pro and registers his photos with the copyright office, you may very well find yourself deep in financial doo-doo.
See
http://thecopyrightzone.com/
One of those guys is a pro photographer, and the other is a full time copyright attorney Their book is on my bookshelf and I've read it twice. (BTW, I've read up on this stuff, and to me it seems like TimSF knows whereof he speaks).
When you hire a photographer most often what you're getting for your money, just as in software licensing, is a license to use that photo or photos for a specific purpose, for a specific circulation, and for a specific period of time.
If someone else wants to use that photo, then you have to pay the photographer for a license that use. Now, sometimes this is remarkably cheap - $1 for for a catalog photo on one of the dollar sites, but it is a legitimate license.
But do not ever just take a photo off the Internet and then use it in your advertising. If the guy is pro, and followed all the registration protocols, to repeat, you may very well end up owing a photographer (and his attorney) well into five figures.
BTW, the book is recommended reading for anyone with even a slight interest it the subject. There is a huge amount of misinformation about it floating around.
Here's a link to a video they made on the topic, a bit over an hour long but it is not a simple subject.