I have 75 interior condos to paint same building all the same color 1 br 2 br 3 br walls,ceiling trim all same color should it be priced per unit and if so how much? Or per sq ft then how much

Are they all in the same condition?
If some will require more prep you may want to go each one.. maybe baseline each one then add on for more time as needed

I agree with mtconc.

Don't let the client assume that any prep work is your work without being more specific. They tend to show you the better ones when they want a bid.

Tell them you need to look through as many as you can, and then make sure specific details, like cracks/holes and other wall/ceiling repair/trim, etc. is done before you paint. If they expect you to do it, you need to account for that work.

If they are new construction, then you prep work starts and stops at priming/base coat and paint coat.

Will you be spraying or otherwise?

I take the square footage to figure out a unit. Add for the extra bedroom. How much tape off will have to be done if spray (is there flooring already installed?) etc.