Multifamily Tax Assessment v/s sale price

[Jackson Sandland]

I"m looking to buy my second investment property. I've got an off-market duplex in a great Milwaukee neighborhood. Houses on either side of the duplex are selling fast for $140k cash, and up. There are two tenants already renting for a total of ~$1500 / month. Some back of the napkin calculations, including all expenses, shows a possible $600 / month profit. Not too shabby. The property is priced around $100k. Here's the rub:
 I checked the property value assessment for 2017, and it's assessed at $50k. 

When investing in multi-families, do you pay attention to the tax assessed value?

Knowing I'd be paying almost twice the tax assessed value is giving me pause b/c there's no built in equity at the time of sale. Appreciation for the neighborhood is very strong as well. It's been going up 20% / year as of late. What do my fellow real estate investors think of this deal?

Thanks!

Jackson