Reverse charging questions 18650 cells

When you connect 18650 cells in parallel, I supose you don't ever have to worry about reverse charging if one cell might become bad? But if you connect them in series, that is where the problem lies.

Now if these cells do have protection, does this mean they are also protected from reverse charging even if used in series?

Last question. How do you know you are buying a geniune cell and not a fake one? I want to buy 3100 Panasonics. They look like this: Do they look real or fake to you that are experts on the matter?

That is all correct. if there is only one cell, or one parellel set of li-ion type cells, the only risk (in the light) is of deep discharging them beyond spec. Which breaks them down internally.
Protection can stop deep discharge in both series and parellel. With protection, reverse charges cannot occur in series because it cant even deep discharge, let alone get the cell inside to 0v.

A cell could have a wrapper put on it to make it look like a panasonic, also even a good cell could be treated like crud by any dealer or distributer before you get it (stored improperly) so it is a good idea to get from a reliable known source.
I have not seen a full running thread on which ones are fake yet (Mabey cloning it hasnt caught on yet). There are 4 sources if you search here that people got panasonic cells wrapped with protection from, that were real. Some of those sources no longer wrap the 3100 just the 3400.