Make sure they do a good job. Paint splashes aren't a 'feature' of the work and should either be cleaned up before you pay or prevented in the first place.

Painting a house from top to bottom is a big job, but worth it financially if you can spare the time.

For example: a typical 4 bedroom house may cost £1500-2000 to paint the interior including materials. This compares to £350-450 for DIY.

If you're not in a rush then try to break the work down into a room a weekend.