Perhaps it should be “A Real Deal”, since “The Real Deal” sometimes connotes singularity, as if there isn’t another deal that’s real. So first of all, what’s “Real” and what’s a “Deal”?
“Real”-ness comes in many flavors. You have your “physically” real, and “mentally” real and, some would say, “spiritually” real. Then there’s “relatively” real. But those definitions are time consuming.
But what’s the point of a “Real Deal”? If something is said to be “real”, why is it categorized as such? To whose benefit is it for something to be real? (Now we’re getting somewhere!) Supposedly if someone says something is real, they are telling you about a phenomenon they have recognized, whether they know what to name it or not, and the information is given to you to use and respond to, as guidance, perhaps, and possibly to help them in some way.
But bottom line: “reality” comes down to significance, and what’s real and significant to you need not be real and significant to someone else. And then what’s a “deal”? It’s a benefit to you. So a “Real Deal” is something someone says will definitely benefit you significantly. And they expect you to believe them.
So you have to determine if you trust them. If they are someone you have known or known of for a long time, you may fully trust them and respond in a manner that meets their expectation. On the other hand, if you don’t know them, you may ignore the information and consider it insignificant, or you may at least give it the “sniff test”, i.e. see if it’s plausible enough to investigate further.
So in my case, if I say something is a “Real Deal”, I would hope that you would give it a “sniff test” at least. Explore further. Try things. Do they make sense? Do they benefit you in any way? I would hope so.