How long should an exterior repaint last?

Almost all the durability in an exterior paint job comes from preparation rather than from the paint itself. Preparation is also more than half the labour, entirely invisible once the job is finished, and therefore the easiest place for a cheap quote to have removed cost. That is the whole dynamic of this trade in one sentence.

What proper preparation involves

1. 1Washing down to remove dirt, chalking and mould, mould must be treated, not painted over.
2. 2Scraping and sanding back everything loose or flaking.
3. 3Spot-priming every area of bare substrate. Different substrates need different primers.
4. 4Filling and making good cracks and gaps, and re-caulking joints.
5. 5Only then the top coats, usually two.

Reading a quote

Ask for the preparation steps to be listed explicitly, along with the number of coats and the actual product. A quote that says 'prepare and paint exterior' is not comparable to anything. Two quotes that both list their steps can be compared honestly, and a large gap between them usually becomes explicable immediately.

Normal weathering, not a defect

North and west elevations take far more ultraviolet exposure in Australia and will always degrade first. One wall chalking while the others look fine is normal rather than a failure, and coastal properties should expect a shorter cycle everywhere because of salt exposure.