I haven't studied the laws of all 50 states, but most if not all laws against receiving stolen property have what is called a "scienter requirement": You must know that the goods were stolen for it to be a crime.
For example, here's the law from my home state of Michigan: "A person shall not buy, receive, possess, conceal, or aid in the concealment of stolen, embezzled, or converted money, goods, or property knowing, or having reason to know or reason to believe, that the money, goods, or property is stolen, embezzled, or converted." https://www.legislature.mi.gov/(S(2ng4lbx1mc0q5rvu2yew3twy))/mileg.aspx?page=GetObject&objectname=mcl-750-535 It goes on to discuss details and penalties, but the point I want to make is "knowing or having reason to know or reason to believe".
If someone approaches you and tells you, "Hey, I just stole this cell phone, must be worth $500 but I'll sell it to you for $50", and you buy it, you've clearly broken the law.
If someone puts an ad on Craigslist or Ebay or some such offering to sell a product and there is no clue that it is stolen and you buy it, you have not committed a crime and cannot be prosecuted.
Theoretically, at least, to convict you of a crime, the prosecutor would have to prove in court that you knew the property was stolen. As you say, that could be difficult to prove. If they don't have video of the thief telling you the product was stolen and you didn't foolish post on Facebook that you got this product real cheap because it was stolen or some such, that could be difficult to prove. "He should have known it was stolen because the price was so low"? Maybe you thought the person was just trying to get some fast cash. "It had someone else's name engraved on it"? The thief could have told you that he bought it from this other person. Etc. Frankly, short of the police actually having heard a conversation in which it was discussed that the item was stolen, I doubt you'd be prosecuted over one item. If you're buying stolen goods every week and re-selling them, different story.
Note that you can be required to return property if it is discovered that something you bought was stolen. Theoretically you could sue the thief who sold it to you to get your money back, but I'm guessing if they tracked the stolen property to you they caught him too and he's going to jail and probably doesn't have any money, so good luck with that. You're probably out whatever you paid for it, but you're not going to jail over it.
Yeah, a frame like you describe shouldn't be possible. One could always speculate about it being done well enough to fool the police, or an incompetent or overzealous prosecutor and judge convicting you even though you're innocent. But you could say that about any crime. You could be framed for murder or kidnapping or whatever even though you're completely innocent.
Update 2 years later
I got drawn back to this post by an upvote, and I see that I never addressed the part about "I could deny that I bought it".
Don't. If you wrote a check or used a credit card, there would be clear evidence. Ok, you say you pay cash. But the police aren't stupid. If they see you withdrew $1000 from the bank on Tuesday and the thief deposited $1000 into his bank on Wednesday, that's going to look very suspicious.
If the item is valuable enough the police could get a warrant to search your house. They could check phone records and see that you called the thief. They could check your internet traffic and see that you viewed the ad for this item. Etc.
If you're caught with the stolen property and you lied to the police about ever having seen it, that's going to make you look very guilty. Much better to say, "Yes, officer, I bought a used TV at a garage sale. I got a great deal on it. Is there a problem?"
I wouldn't be so bold as to say that it's always best to tell the truth. Ignoring the moral issue, there are certainly times that you can lie your way out of a problem. But this is a time when you are better served by telling the truth.