So sustained maintenance should not be your concern, your concern should be on how fast you can recover the initial cost of the hot tub, the maintenance is not the issue.Argument #2 Seems like this is based out of fear and the unknown.  

And the investment is tied up for an unknown number of years - estimated to be about five more years but no one actually knows!

While you actually may be just opening from one rabbit hole of headache from left pocket to  another rabbit hole headache into the right pocket, all these investment has known and unknown risk which could eat  our soul and financial if we don't understand of what we're doing.this is why in biggerpocket i no longer curious or think if someone has 9999 doort.

Sometimes the risk (self-install) outweighs the reward (saving money) especially if there is an unknown factor with the tenants ability to do the install. 

If outlined in your lease clearly, my method should prove effective; if a tenant complains about wrongful withholding of the security deposit for an unknown water bill, that withholding dispute will be resolved before it can go anywhere. 

Flips are more ‘unknown and one off income events.”  

Old houses have many unknowns and always go over budget.

I was sharing with the OP that buying cheap properties in unknown markets in the Midwest (or South) is definitely not passive and may cost more money in the long run with not enough appreciation to make up for those losses. 

Do I stick with my realtor for this deal and keep waiting an unknown period of time until I hopefully receive a respectable offer or do I run with the seller finance deal.

At least in NJ its always "buyer beware" (the onus is truly on the buyer) so its used as reminder especially in situations where there is a higher risk or more unknowns from the seller.