How to calculate exit price on an apartment building with regard to property taxes.

[Joseph Graeve]

When you are purchasing a multifamily property, the seller will be advertising the property performs at a certain cap rate. Their cap rate is based (among other things) on the current property taxes that they pay. If I were to purchase (at a higher price) then the taxes I pay would be very different from their taxes. So how do you normally approach these conversations when you are negotating. If the seller says "its a solid 7 cap" and its more of a 5-6 cap after you purchase and the taxes go up, do you mention it?
More importantly, when you are looking at your exit scenario of selling, the same question applies but in reverse, are you calculating the new tax rate the next buyer will pay and reverse calculating a sale price based on the market cap rate? Or do you figure a sale price based on market cap rate but with the property tax expense you pay currently?