Okay, so ... how do you tell?
If it's less like what you'd like it to be, the greater the probability that it is in fact real, unless... it involves unusual or unlikely combinations: example - Tyrannasaurus Rex invades your bedroom.
At what point are you conscious that you've been dreaming? Is it when you wake up, or have you realised the dream quality during it? Would you still recognise it if that quality was suppressed as a result of dream credibility? Are all dreams ridiculous in some way?
They could be primitive and functional rehearsals, "What would you do?" scenarios.
Take the first example, would you debate whether or not to battle with a T-Rex, or decide you've had enough of that dream and now is a good time to wake up?
Technically and evolutionary speaking, that's a huge use of time and resources maximised.
Consider, the basics....
It's a rehearsal - all sensory experiences can be inclusive, motor muscles respond to stimuli, rapid eye movement (assessment).
You appear dead during the stage of paralysis and you're totally unaware of what's happening. (this has huge implications in survival technique and human evolution) - yet your ears aren't 'off,' so although you appear dead, your brain is still processing sound. You'll wake up immediately if there's an unusual noise or continuous one like workmen drilling a hole at 8:30am on a Sunday morning.
A Primitive being is in control that is aware of the implications, motivation is paramount and parallel with success.
