I want to buy new speakers for 50,000 and see it used for 30,000, what should I do?

The OP’s B&W vs Sonus faber are very different sounding speakers.

Although I demoed several B&W 800s speakers, didn’t resonate with me and seemed bright.  Sonus faber is much more musical which translates to engaging.  Although we all have our personal preferences in speaker sonics, hard to imagine the OP not liking the Sonus faber

Bump, how did I miss this thread? My dilemma with the used +$50k speakers is how they'll sound in my room, with my components? My current speakers do nicely wity my $25k Mac front end, but what if those new speakers actually need the CH precision, Solution, Chord or gasp MSB components with $7-10k acc's to really get there?

I saved $25k on the speakers, but now have to shell out another $50-75k in used components and treatments. 

Every B&M dealer I've worked with has extended the offer to let me bring my gear in to hear and a couple dealers have even let me home demo speakers if they have demos on the floor. 

Once I start whittling away at the dealers price I'm trading their service in for a better bottom line and I don't have the experience they do with their products.

  Sometimes I think, if I could hire my dealer to set up my current system he could probably make it sound better than anything I bought at any price and set up myself.

There are a lot of really great speakers out there that are almost new for a significant discount. Dealer demos (ask them not to put “demo” on the receipt for future warranty, trade ins or open box. My last set was 15k and were as brand new for 10k.

it allows me to build a better system cor less and when i sell or trade the loss is much more palatable. 

If there is no reason to believe the used speakers are in less than excellent cosmetic and operating condition, and you can know their provenance (i.e., not stolen or bought from a flood salvage liquidator,) buying the speakers at $30K reduces your loss on resale if you don't want to keep them. Speakers last a long time if well cared-for (and not stuck in a storage or a musty basement somewhere.)

At $30K, I would insist on being able to travel to see them and hear them and if you buy them, being able to specify how they will be transported to you. Anything short of that would be a hard pass.

I can’t believe it’s not butta.