It currently generates $1350 in gross rental income. 

My city requires you to submit gross receipts and fee is calculated at $0.16 per $100, and city said gross receipts is the sales price.

(Partnership with a Broker)I have a meeting with the current owner set up and I am curious on questions I should ask.Currently they have 115 doors that they manage. 4 employees(2 are willing to stay) gross income last year was around 180,000$.

. $2600 x 12 = $31,200 Potential Gross IncomeLess Vacancy/Collection Losses of 5% = $29,640 Effective Gross Income$1250/mo = $15000/yr in Operating Expenses$29640 EGI -$15,000 OE = $14,640 Net Operating Income$14640 NOI divided by $280k purchase price = 5.22% Cap RatePut another way, if you invest $280k in this property, you will see a 5.22% annual return. $280k x 5.22% = $14616 (the other $24 is just a rounding error from not carrying out the decimals)There is literally no other correct way to calculate cap rate.https://www.biggerpockets.com/...

The mortgage statement will tell them at least part of that story and with a little math to remove a percentage of the gross, they'll know if you're in over your head and if the property is a boat anchor or not. 

Works out real well, my gross is 2 times the norm and I don’t deal with lower quality tenants which is the duplex norm around here.  

I’ve heard of people buying cabins over the $600,000 mark with an expected gross profit of $100,000.

GP meaning Gross Profit?

Then there are adjustments for things like property type, loan amount, prepayment penalty term, location, the DSCR (debt-service coverage ratio (basically the cash-flow) which you get by dividing Gross Rent by PITIA). 

Gross monthly income is estimated to be $2000-2150 upon moving out.