Cap Rate Calculation Question

[N/A N/A]

Ive come across a property in my city that is currently mixed use ( one office and 3 luxury apartments) listed at 399,900. Current Data are:

NOI using previous tax assessments is 37,000 per year
Annual Rents are 43,200 per year

Current accepted cap rate for comparable sales in the past year is 10%
With these numbers, the sellers are using a cap rate of approximately 9.25% BUT using previously ridiculously low property tax payments of 2400 per year. At the new sale price the new annual taxes would be 16,000 skewing the whole calculation. I used a small homegrown calculation for two adjusting variables to figure out a reasonable price given a 10% cap rate and 4% property tax rate and the same gross rent rate to give me a price of $289,000

My question is.. do I calculate this new price or any reasonable price based on previous tax assessments or use whatever the new assessed value would be, ie sale price.. this vastly changes valuation and my initial offer..
thanks in advance! :beer: