Executive level- worth it? Any limitations to buying points in the secondary market?

I have a platinum week at marriot mountainside, and converted to the points program. My week translates to 5300 points. Marriott always trying to upsell, is offering 1700 points for $22k (roughly), putting me into the Exec level which does seem to have some very good added benefits. So- quick poking around I see this number of points in the resale marketplace for $6900 (one ad) and wondering what the difference is and/or any limitations in buying in the secondary market? We've enjoyed our timeshare and the points program seems to offer us needed flexibility but that said, I find the whole process to be very confusing and tough to stay on top of. Appreciate any advice or thoughts Thanks

This article may provide you with some good information, including benefits that transfer or don't transfer with a Marriott resale: Marriott VC Resales

That was a very helpful article, thank you.

There don't appear to be any limitations in buying the points in the secondary market to get to Exec level, and it looks like it would be roughly half the cost vs buying from Marriott (at $14.24 per point as quoted two days ago to me)

So, it begs a further question. Who are the most reputable (and competitive) sellers of points in the secondary market?

We have MVC point resale postings on this page: MVC Point Resale Postings