Sometimes it's the importers that are at fault although they may be ignorant of the facts, too. You can't trust on-line product listings, either, as they're probably the worst offenders. You'll find many products listed as shorea or nyotah (the most popular I've seen) and they state they're either as tough as teak or a "relative" of teak. Some producers are even borrowing the word teak as in "Amazon teak." None of these is the real thing.
Teak is divided into classes: A-grade, B-grade, and C-grade. Differences are minor; you might see less uniformity in color, but it still retains natural teak strengths. Also, the lesser grades are harvested earlier, say, at 20 years instead of 40 years. Just be sure you know what you're getting because you still don't want to pay for A-grade if you're getting C-grade. You may find Indonesian imports claiming to be A-grade. This may or may not be the case. Unfortunately, those are chances you take with on-line shopping.
Another tactic is chemical dipping. Manufacturers take lesser grade woods and dip them to look like top grades. Some will state they've done so; others will not.
Indonesia is the largest exporter and officials have taken great measures to provide sustainable plantation-grown resources. Still, teak is rare compared to other species and that's why you pay the price. But if it matters, teak should last well past the owner's lifetime while other species can’t live up to that claim.
Photo courtesy morguefile