I am renting out my townhouse while stationed overseas and have had 2 different tenants within the last 2 years. After they moved out, the interior was completely repainted twice using the same contractor. The whole interior is painted white with a flat, no-gloss latex paint with the exception of the bathrooms- semi-gloss paint.
Would it be possible to just do touch-ups rather than repaint for such brief periods of occupancy, since repainting everything is very expensive. If the painter decided to just cover over any mars and smudges using leftover paint from the previous job using the same application method, would there be any way of detecting it?
Usually, when I'm in doubt whether to touch-up or full paint..go for the full paint. In your particular case, your trying to impress potential renters. Its also about smell, the freshness, new townhouse feel.
However, cost being a major factor these days, I have done many successful touch-ups. Since the exact same paint is going to be used, I would thin it with water a bit first.