Mark covers it really - with micro blisters probably need a complete respray, with gelcoat cracks it depend son how many and how big. A few other potential paint issues include
Dull & faded - can often be polished out, but depends on the thickness of the paint. Red is worst colour for fading. Same for light scratches in the paint, especially likely if a previous owner has used car washes or been over-enthusiastic with the chamois.
Sink marks - where solvents are gradually released from the paint, and the top layer 'sinks' to show the repairs underneath. These can take over 6 months to show after a respray. Slight sink marks may be polished out, but probably will need filling and repainting
If repainted, what paint was used - cellulose paint can be spot repaired, and blended in to the original (useful with a small sink mark or run). More recent 2 pack paint is a lot harder, and will require at least the entire panel to be repainted. Check for subtly differing colours along the car - signs that panels have been repainted or spot repairs done
As Mark said - if it looks good enough for you, then any blemishes are negotiating points. Otherwise could be expensive (from ?1k for a quick 'blow over' to ten times that for a quality respray), or if you have the time, space and equipment, then respraying a car is around ?200 paint and thinners. Sandpaper costs depend on the amount or work required, from a light preparation (couple of hours) to a complete rub back to gel-coat (months of hard work, been there, done that
)
Peter