Let's say a person has a lawn that is 75% grass, 20% a wide variety of
weeds, mostly clover but also dandelions (mostly pulled) and few
different types of broad leaf weeds (mostly pulled) and 5% bare
(mostly because hours were spent pulling patches of dandelions and
broad leaf weeds,

Let's say this lawn is 30' x 50'.

Let's say the owner would like 100% grass, 0% weeds and 0% bare spots.

Can this be done with a "weed-and-feed" product, some overseeding and
diligent watering or does the owner need to start from scratch?

If the owner needs to start from scratch, can the existing
"everything" be rototilled under or do all of the weeds (and grass?)
have to be killed off first?

I might as well mention the soil condition. I'm pretty sure that the
soil could use some work, but the owner is on a very limited budget
and probably can't afford to have 30' x 50' x 3" of top soil brought
in. I can get the soil tested for her so we know what we're up
against.

I can line up labor from various sources to help the owner out with
tilling, seeding, watering, etc. but asking for actual cash for top
soil and other rmajor treatments is not going to work.

What are her options? Thanks!