It is very important to have good pictures available of a watch you're looking to buy.  It states several things: that the seller is being open and honest about the sale by providing you a clear picture for inspection, and more importantly that the seller isn't trying to hide something by posting fuzzy pictures that obscure details.

Always look for pictures that show a watch at different angles. You want to see clearly the dial, case back, band or strap, and the clasp.   By having clear pictures of these features it's easy to compare them to known genuine examples as well as look for flaws such as scratches, scrapes, and general wear.

Poor pictures provide you no assistance and actually harm the seller by withholding information.  If you have any doubts about a watch because of the pictures tell the seller that you're interested in the item but you would like to see some additional photographs.   One of the tricks you can use is to ask the seller to set the date or time to something specific to make sure that the pictures are actually of the watch they are selling.

Be aware that some unscrupulous people will use photos of other watches and represent them as their own.  When this happens you're never sure of what you will actually get from the transaction; it could be a real watch, replica, or worse, nothing.  Always feel free to ask the seller for additional pictures.   His response will aid in making your choice.

My rule is that when the pictures are poor to pass on the auction.  It's typically a sign of some kind of deception.   Still, if the watch is what you want ask the seller for additional photographs to help you gather the information you need.

The Seller's Description

The description the seller provides is your only source of detailed information about the watch in question.  You should look for detailed information about the condition of the watch, as well as exactly what comes with the purchase: i.e. box, papers, and paraphernalia.  Details are a good sign that the seller knows what he has and finds it important that you the potential buyer have enough information to make an informed decision. I avoid auctions with terse uninformative descriptions like the plague.

When attempting to settle disputes over a transaction, sometimes buyers will refer to the description when describing misinformation or out and out fraud.   Many disreputable sellers will try to hedge their bets by phrasing the description in a way where they can imply they were unaware of the authenticity of the watch.   Common examples are:

"I bought the watch at an estate sale."

"It belonged to my grandfather who just passed."

"I got the watch as a gift from work."

"I'm selling it for a friend."

"I don't have the box or papers, but my jeweler said it was authentic."

"I can't vouch for the authenticity so bid accordingly."

"I'm no watch expert, but it looks real to me."

"This was my ex-boyfriend's watch and I just want to get rid of it."

And many more; the gist of it is the seller is unable or unwilling to fully vouch for the watch.  This typically points to the fact that they are fully aware the watch is a replica; they're just hoping you'll swallow the bait and ignore the caveat.

While even if the original box and paperwork is supplied with the watch these things can (and have) been forged or faked.   There is a market in replica Rolex boxes around the world; you can buy one for $25.  While not exact to the genuine Rolex they may pass as real in a photograph that doesn't focus on their details. Still, close ups of the paperwork (including the signed warranty card) are great.   A copy of the sales receipt also adds credibility.