When they sell an expensive property, they have money left over to bid up properties in Arizona and live in much larger and nicer houses in better neighborhoods.Anybody who already has properties in Arizona has done quite nicely.

The rental agreement should cover cost items that the tenant is responsible for paying - consequently any cost left over is covered by the owner.

I generally max 401k, max backdoor roth ira conversion, max hsa, taxable brokerage, kids 529 through the state, then invest in RE with the leftovers.

ive got a potential seller with an existing mortgage left over of 190k an the home arv is abt 310k how would i go about my offer price formula with the existing mortgage? 

This would allow you to purchase 7 with money left over.  7 * $237k= $1.659m. - same condition above today has max LTV of 95% allowing 15 purchases with the $100k.  15*$237k=$3.55m

If there's money left over, refund it.

I could sell it yes and there would be a lot more than $150 left over.

There were also clothes left over from a previous guest.  

Of course, nothing is stopping you from selling Rental #1, paying taxes, and then taking your leftover after-tax profit and moving that into Rental #2. 

Why its so important because the appraisal better come back with at least 20-25% equity left over so you can pull the money you used to purchase it and do the repairs.That said, you can use cash, get ahold of a hard money lender ( most expensive option), or get seller financing.