Firstly, there's no such thing as a "Lucky Guess" that is an excuse skeptics use in order to sustain their delusion that nothing is real.
Secondly, the Wall Paper message was for you more than it was for anyone; it is what we call a "convincer" in the biz.
I've done work as a professional Reader since the latter 1970s, there's not a year that goes by that I don't have a dozen or so sessions that reveal uncanny and quite specific details about a client or someone the client's tied to in life that neither of us had any possible way of knowing about in advance; the information wasn't jiving with the sitter and yet clarity would take root, sometimes during the Reading itself or within a day or two of the Reading. In that I do record my session (contrary to the claims of most skeptics many psychics do offer a recording to clients) it was quite easy to take an objective look at such things and count the number of accuracies. . . not vague and "maybe" hits but solid and direct connections.
No, this does not mean that it happens with every sitter -- IT DOESN'T! and any psychic that says otherwise is full of crap; the gift doesn't work that way even though it will give clients insight to what they "need" to know at the moment vs. what they may want to know. This is frequently the problem with Psychic work in that we aren't "Prophets", we're READERS -- we translate information as best we can based on what is shown to us via which ever system we work with. When it comes to Mediumship I'm far more skeptical, but I have had experiences in that arena that scared the hell out of me and still make me ponder why anyone would want to have that sort of connection with any kind of disembodied entity -- it's simply creepy and nauseating as far as I'm concerned.
Very few people know what "Cold Reading" actually is or isn't even within the world of the know-it-all magician. For starters, if you're basing your idea of what it means based on the works of Joe Nichol, James Randi or Ian Rowland you're automatically screwed in that none of them honestly know what they're saying; two of the three have NEVER done any kind of work as a professional Reader so what they say is psycho-babble and speculation. Randi actually did work as a Psychic but was outed because he was so bad at it; his reaction to said rejection was to lash out with tremendous venom. . . it was a slightly delayed response however, it would take his being rejected by a certain kid from Israel to really light that fire back in the late 1960s/early 70s. Randi wanted to manage the kid and his U.S. Tour while Uri thought it a bad move. . . or so goes the story (not the JREF approved spin).
To be a true skeptic one need question those "authorities" that attempt to convince you that the devil doesn't exist just as much as you deconstruct the issues that bring you challenge.