If they want a great shine and a maintainable finish, I would throw down two or three coats of Johnson's diversey fortify concrete sealer. Followed up by two or three coats of Johnsons signature. It should pop if the floor isnt too open or rough.
I would just go with some of Johnson's Fortify. It will look great and it holds up well.
I would have to strongly disagree with putting Signature on it after Fortify. Unless they are going to regularly maintain it and high speed burnish it will scratch up and look like heck quick!
I've used Fortify for years on etched concrete and it performs very well.
I agree, especially now that I see the floor. It would be in your best interest to try hard and find out what is currenty on the floor now, perform a heavy scrubb and lay Agee more coats down.
Unless they were unhappy with the way it looked when the last application of sealer was done.