@Benjamin CowlesYeah, you have to decide what makes sense for them to repair vs. what makes sense for you to repair.If they are on the hook for things they might break or clog up then you won't be getting calls at 2AM for minor stuff.However, if you show up to the house one day and they've installed new flooring or other items they can't take with them when they leave (this happened to my folks years back on a rental), then they might try to claim they added value to the property and have something at stake. 

David,You have just swept the floor clean with this post.

We are going to be removing 2 walls, renovating the kitchen, one bathroom and all new flooring and paint.

We basically do everything drywall,paint, siding,gutters, concrete,tile, carpet, vinyl, hardwood flooring, fences,landscaping, tree service, asphalt,electrical,plumbing,carpentry.

Question, whether for flip or rent, should I get existing flooring removed completely or just put additional flooring over it?

But neither can be accurate if they don't take into account the floor plan, condition of the mechanicals (electric, plumbing, HVAC) and structure (roof, gutters/drainage system, foundation, doors, windows, walls, woodwork, special features) and furnishings (cabinetry, floor coverings, window coverings, appliances, lighting fixtures, plumbing fixtures) and land (zoning, location, yard size, landscaping, fencing, nearby attractions/distractions).

How is your experience with laminate flooring in rental units?

Replacing a broken floor tile is a repair, replacing the entire floor (while preserving the original value) adds life to the flooring as it's entirely new. 

However if the house has a few decades of age and the floors are fairly flat and level and the walls fairly plumb (not perfect, just not way out), and there are no horizontal cracks visible in the walls or concrete, then you don't likely have a foundation problem.

It's located in one of the most desirable and fastest growing school districts in the area.Each of the 4 duplexes (8 units) have a 2 bedroom/1 Bath/1 carport with nice wood vinyl floors, upgraded kitchen and bathroom.