Should identical properties on same rd have different cap rates?

[Christa S Rickard]

I know there are a bunch of posts about cap rate and I've read quite a few. However, every time I think I understand, I'll see something in a listing that confuses me. 

My current interpretation is that a cap rate is set by the market - meaning it reflects what sellers are willing to pay for a property/return on investment. So in hot markets, cap rates will drop and sales prices go up because people are willing to pay more for a property. In 'cool' markets, the cap rates increase and sales prices drop because not many people are buying or they are holding out for better deals.   

If that is correct, then if I have 2 identical properties next to each other on the same street, in the same condition, shouldn't they be the same cap rate?

I received a small portfolio of off-market properties for review. The seller is in the process of doing some upgrades before listing them so I'm trying to make an offer before upgrades are finished. Given my luck thus far, I'm not holding my breath for success but I am hopeful.  

Two of the properties are 8 units each. Both properties are right beside each other on the same street. Both are pitched roofs with brick exterior. Both are fully rented. The leases in both units are below market by varying degrees - the annual gross rent on the one is about $3k more than the other. Also, the one has $1k more in property tax than the other. 

The seller sent separate financials for each property. Barring the taxes and rental income, all other fees are the same between the two. The list/sales price is also the same price for each property but they are using a 6.6% cap for the one and a 7.5% cap for the other. Shouldn't they both be either 6.6% or 7.5%? I think they are only changing the cap rates so that mathematically both properties keep the same sales price. However, that's not how cap rates work, is it? I thought they were the one thing that should be fairly constant between property types/location/quality so that you had a consistent way to determine value?