Never ever eat unripe fruit, it messes up your digestive system terribly, and it has no/low calories and no/low nutrition. Ripe means super duper sweet with no hint of sourness.
There is absolutely no way to find ripe oranges/tangerines/clementines in commercial sources, if you want them ripe you have to have a tree of your own in a decent climate... correct?
They are often unripe but you can find them ripe, usually half way into their season. Same with most other fruits. Grapes for example, when first of the season they are so sour but I start taste testing them at the store about 3 weeks in and sometimes find good ones. Except for stone fruits. I find that the first week or so they are out they are great and will ripen up quite well but after that they start picking them so early that they will never ripen. :(
Oranges are one that do not ripen once picked. You can let them sit and the sourness will fade but that is not ripening, the sweetness will never increase.
The fruit quality is dwindling every year because consumers don't know what ripe is and they do not return bad fruit or complain. So do your part and return bad fruit and complain!!! :)