The main Ocotlán [1] attraction (unless you’re lucky enough to arrive for the big fiesta on the third Sunday of May) is the huge Friday market. Beneath a riot of colored awnings, hordes of merchandise—much modern stuff, but also plenty of old-fashioned goodies—load a host of tables and street-laid mats.
How about a saddle for your donkey? If not that, why not four or five turkeys, a goat, or perhaps half a dozen bags of hard-to-get wild medicinal plants? And be sure to pick up a kilo or two of cal (lime or quicklime) for soaking your corn.
If you’re looking for lots of native costumes, you’ll have to head for the mountains, because few women (except for their ribbon-decorated braids) and virtually no men wear traje. You’ll hear plenty of Zapotec, however. At least half of the local people are native speakers.
Since markets are best in the morning, you should make Ocotlán [1] your first Friday stop.
Links:
[1] http://www.moon.com/destinations/oaxaca/oaxaca-valley/south-crafts-route/ocotlan