Collecting Peace ....considering Buying A Set

I would be wary of inadvertantly purchasing an altered 28-s in a complete set, as that coin would make up much of the value. Even with a return policy, the seller might say that you switched coins if you return(It's easier to make that claim with full sets). I'm just trying to look at the worst possible situation. Other than that, I see nothing wrong with that approach. You might considering purchasing a set that is intentionally missing the 28, just to be safe, and be cheaper.

I would guess you can get a complete AU set for around $1500. As said before, you need to be cautious with the 1928-p

I sell sets at coin shows all the time, even on E-bay.
But to ensure that you are purchasing a "AU" coin you should look
local. Using your method of purchasing 2 sets and combing them would cost you 1,200 - 1,500 each. That is close to $3,000.00. You want to
get some of your money back for the un-used coins. Attempting to sell
cleaned and altered coins are hard pressed, you will take a loss.
You are better off with the money back policy and purchase
AU to MS coins at auction then combine your set. You will save money, by not having to attempt to sell off unused coins. Your money is protected if you do get a cleaned or altered coin.
I know this as I sell SLAB PCGS common date Peace dollars as MS 62 for 30 to 40 dollars. Taking your time and be picky with your selection, later you will not have to up-grade. My self I now have a
ms 65 and above collection I am putting together. Evan though I'm a dealer I still have the love of collecting.