Be very suspicious of all health claims from people who are trying to sell you something. It would probably be better not to read them at all, though I do kind of enjoy the obligatory blurb on all tea stores' websites about how their tea "purifies the blood" and removes unspecified "toxins," whatever those are.
As far as I know, it is still debated whether dietary antioxidants actually provide any significant health benefit. Many studies have concluded that they don't. And there's also the issue of bioavailability: even if a given food contains lots of antioxidants or other good things, you may or may not be able to absorb them, depending on other chemicals in the food, how it's processed and cooked, what else you eat, etc.
I would say: eat/drink things that taste good, because being happy is good for you. Eating vegetables is probably good too, but there are no cure-alls. (Luckily tea tastes good...and it's a vegetable, right?)
If you have access to a library:Olive tree (Olea europaea) leaves: potential beneficial effects on human health.And 345 more.