IF you do not understand who the different sellers/resellers are, why their prices may differ, and reasons for differences in domestic vs international prices -- then, you most likely are not ready to use gear since you failed to do even the most basic research regarding your potential sources.
Wouldn't you want to spend some time (not days, I mean weeks+) really understanding what you are using and where it is coming from?
and, checking the track record, first hand for yourself, over the entire duration the source has been active to evaluate if the source looks worth taking the risk?
After doing things like that, basic first steps at researching a source, you would already have the answers to many of these basic questions being asked daily.
Even then there is no guarantee; but I know for me that I would want to do my own research instead of just go off of what some random guy online that replies to one post says.