Don't buy property in Sète if you're looking for traditional charm or tranquility. Sète is a small city, not a town, and has the traffic (especially in summer), noise and modern conveniences to match. It's also very much a fishing city, so the smell from the harbour can sometimes be rather off-putting.
The town itself is actually not all that nice - certainly not as charming as Pézenas, for example, or as intimate as Marseillan. Apart from the expensive villas on the hill, you'll find apartments in old town houses here, or entire town houses, which you can renovate to add value. Around the edges of the town, a number of property developments are appearing, most of which are relatively up-market, due to the relatively higher house prices here, and the premium that comes with a view of the sea.
Property in Sète would make for a good investment, however. Prices here rose by 10% here last year, and are expected to continue to rise. Most of the Languedoc coast is very flat and rather uninteresting, rising only at Sète, Agde, Gruissan and Collioure, so these spots tend to be more expensive. Sète is also close to the A9 motorway, and only about 30 minutes' drive from Montpellier and Beziers airports.
Of course, you could buy a house or villa just outside the town of Sète itself. Frontignan (where they make superb Muscat) to the north is not bad, with quite a nice beach nearby. Balaruc-les-Bains isn't terribly nice, and nor is La Peyrade, both being too industrial. Mèze and Bouzigues, however, just behind Sète on the Etang de Thau are both very pretty, with spectacular views across the oyster beds.
If you are looking for something on the coast that's a little quieter and cheaper, try Gruissan and Leucate, just south of Narbonne. If you want the lively hubbub of Sète without the traffic and smell, try La Grande Motte further north.
Should you not find the property for sale in Sète that you're Looking for, why not contact an estate agent in the area to see what they have to offer.