It's sell, take the 100k profit, your at 360k in the bank, VTSAX or money market and chill for a bit, see how this market/economy thing plays out, rates have to come down no one can afford at these rates, then maybe look to refi and get the rate under 5%.Also something to think about.....

a) everyone can use a pool, b) not everyone can or will use a pickleball court c) almost everyone who is a bit older who started playing pickleball ended up injuring themselves, d) a pool is a lot prettier and adds a lot of ambiance to a backyard.

All you'd need at that point would be RE attorneys for the contract and formalities.To find recommendations on seller financing deal structure, I'd start right here on BiggerPockets by using the SEARCH feature and playing around with different keywords i.e. owner financing, seller finance deal structure, seller finance terms, owner finance terms, etc.All the best!

That's probably not a pure parking play though.   

Would this be a slum lord play?

You may have a grasp on this aspect, but there are items to consider that can play a big factor when choosing your land such as topography, existing zoning & platted lot status, minimum/maximum requirements such as parking, detention, size of building, setbacks.  

If he's getting 10-12% return, why not borrow at 8% and play the spread?

Income over many years-weather plays a big part is the success of a wash, you want to see REAL numbers for st least 3, more like 5 or 7 years to get a better picture.Sellers mindset-is he really selling 2 of 3.

Landlords who pay attention, are ready to wait, play by the rules of the local laws, and have enough volume or cushion to ride out the outlier experiences, have seen, and I believe will continue to see, the benefits of lack of competition accrue to them to the tune of millions of dollars. 

Is that the play?