Older properties... 80 - 100+ yr old and uneven floors...

Recently, I have come across a few properties that are 100+ yrs old with lot of uneven floors.  Been reading a lot on how to even out those floors with lot of different and conflicting point of views.  So my question is multifold. 

What steps do you guys take when you come across such properties? Do you always get a structural engineer to go through the property and make sure everything is OK from structural POV and nothing is structurally bad with the property.  No idea how much a structural engineer would cost, but I am thinking around $1000.00 to do the analysis? 

Also, what steps do you guys take to even out the floors?