Is it possible for a true caster (wizard, cleric, etc.) to pretend that they were actually casting a spell off of a scroll? How about a fake wand?

The purpose would be to conceal the fact that they were a true spellcaster, rather than eg. a rogue. I imagine that some sort of spellcraft check (for others) might be involved.

You generally wouldn't be able to do this, unless a spell description states that the only component is verbal, or you have still spell feat.

Casting spells generally involves a lot of complex hand movements and material components, which are not required when reading a scroll.

In game terms, it would be very tough to do since what you see is what you get, and the animation for casting is very different from reading a scroll.

I am not even sure if it's possible, but you could try casting a Stilled spell at the same time as using the 'read' emote, which I think exists somewhere!