The kitchen tiles and cabinets like at least late 80's or 90's.

When I read that, I immediately think they must be working in the deep South, or FL or somewhere where the median home cost is under $100k.My belief is that if I am going to put reasonably high quality cabinets, floors, appliances and trim into homes, shouldn't my profit reflect the extra investment in materials and extra time to do the finishes?

All of these have their own costs associated with them.When everything is said and done, it comes down to YOUR decision......If it's a small rehab job, couple of rooms of drywall patch, paint, kitchen cabinets and flooring, put the HVAC system in and clean the duct work afterwards.  

Water and drain pipes have already been plumbed for the kitchenette, so all that needs to be done is the installation of cabinets, sink, toilet, vanity.The way I see it, I have a choice:1.

I believe the cost was $80-$90/sqft depending on finish & I believe the buyers were supplying their own kitchen cabinets & windows.

Same in the kitchen,  I've been running a wire from the ceiling box to the cabs and installing cheap LED under cabinet lighting that goes on with the overhead.

Both of them have considerable experience taking down/ putting up walls, installing cabinets/fixtures.

@Scott England The property itself will be residential (1-4 units) and will be rent ready or very minimal updates (paint, refinish cabinets if needed, etc.)

I usually estimate based on the cost of materials and do the work myself, for example:used or new toilet: $20-$90plain white sink at lowes (order online): $40used or new window: $20-150used or new door: $20-150bathroom mirror: $10-20sheet of drywall: $10bucket of mud: $12sheet of 1/2" plywood: $20laminate or tile flooring: 1-2/sq.ft.5 gal of paint, primer or polyurethane: $50-100used or new cabinets: $0-600laminate countertop: $50-200used fridge and stove: $100-260new water heater: $220If you don't know how to make certain repairs there are lots of youtube videos that you can learn from.

There are electricians, plumbers, the general contractor's crew, cabinet installers, etc.