If you know what you are looking for, you can typically pick up an off-center freebore with the naked eye (within reason). As a quick check I look through the clean (unfired) barrel and make sure the little ledge at the end of the freebore is visible all the way around and there are no traces of rifling left in the freebore area. If there are traces of rifling (not bad, just a large groove diameter barrel) make sure they are even all the way around.
Same goes for a borescope........evenness is key. Also, I've seen freebores that are cleanly cut all the way around still have enough "lumpiness" to stick bullets and cause issues. Typically, you can spot this by looking at the ream termination in the groove......rounded is bad.......straight is good.
Please keep in mind these are very miniscule characteristics that rely heavily on the shape/size perfection of the barrel interior.
I still feel that a shit ton of shops big and small are unaware of this issue or don't know how to avoid it or check for it. Hell, I was unaware for a long time myself even while working for a top shelf builder for almost a decade. I recently saw a rifle from that same builder with a severe case of this.......they blamed it on a "bad reamer"......go figure. At least they took it back and made it right, the rifle owner is happy now.
It never ceases to amaze me that barrelmakers can drill/ream/rifle a hole through a solid bar 30"+ long and machine monkeys like me can install them and get the accuracy we do.........it's not like we are spending Uncle Sam F22 money to get it done either.
God Bless America