Repairing or replacing a concrete patio
A few hairline cracks in a patio that's still level and draining usually aren't a reason to tear it out, and I'll say so at the estimate. When the slab has sunk, tipped toward the house or broken into pieces that rock underfoot, the trouble is usually the base underneath, and patching the top won't fix that. In those cases, breaking it out and rebuilding on packed ground is usually the better use of your money.
What shapes the cost of a concrete patio
Two patios of the same size can cost quite differently once we see the ground, because soft or low spots mean more digging and more fill. Thickness matters too, since a slab that carries heavier loads takes more concrete. When a budget is tight, people often want to trim the base work first because nobody sees it on day one. I'd rather you make the patio a little smaller, because a thin base shows up later as sinking and cracks.