This does not address your question, but I am posing another - Does the basement have ground level access for an inlaw suite so there is egress and typical stairs are not necessary? I am asking from perspective of already dealing with aging relatives.

you could try and DIY it. You can buy bags of self-leveler, mix to the consistency of melted ice cream, and pour. It finds it's own level. My hubs and I did it in our 1800sf house. You probably wouldn't have to do the whole floor just the really bad areas

Have your floor guy mark his areas of concern for you. If he won't, it's easy enough to do with a long level. Just run it along the floor, find the dips, outline with spray paint, mix, and pour.

Custom Building Products LevelQuik RS 50 lbs. Self-Leveling Underlayment-LQ50 - The Home Depot

You could also sell your flooring to someone and get carpet.

Or, try and contact the manufacturer and ask how much flex is in their flooring.

Sounds like a perfectly reasonable amount based on how out of level your slab is. Read the spec on your floors, they require the slab to be within certain tolerances.

"Read the spec on your floors, they require the slab to be within certain tolerances."

Or when it the click locks break, the floor moves and the boards start to pop up there is no warranty.

I'm going to say that you have ONE HECK of a decent flooring installer working for you!!!! No. I'm not kidding. I would say 95% - 99% of the time a flooring 'dude' (or some guy who swings a hammer who told you s/he could install flooring) just throws it down and runs for the hills.

You have an honest person working for you. The quote he gave included a LITTLE bit of levelling. Your concrete is NOT good enough to have 'spot' patching done.

I've always suggested to my customers to budget $2 - $5/sf for CONCRETE slabs. Your quote for concrete work = $2/sf. That's RIGHT ON TARGET.

Good to know that you have TWO honest performers here. Yes, concrete is a B!TCH to deal with. Yes vinyl needs FLAT...but then again so does laminate, hardwood, tile, etc. The ONLY things that do NOT need flat = sheet vinyl, sheet linoleum and carpet. Yep. The things that role out and that can wrap around a telephone pole.

So...you have THOUSANDS of dollars worth of flooring (I'm guessing around $4500 - $6000). That is MORE expensive to waste than it is to install. Right now you have a wonky concrete subfloor. That is normal and to be expected in a basement.

You will only pay for this leveling ONCE. After that you will have a great surface to work with for the next 60 years. The concrete slab guys will get you a much better surface. The INSTALLER will then do the 'few' patches he has quoted for you. The two put together will create the 'acceptable surface' you need to put down ANYTHING OTHER THAN carpet.

That needs grinding of the high dpots first. Then filling the low spots. Its cheaper to fo it right from the beginning rather than have all the flooring fail and then have to level, and buy new flooring too.

Follow manufacturer's guidelines as suggested.