I am being a bit anal about my PMs. I buy (so far) only new stuff, then seal it in individual bags - even the low premium stuff. Other than coins bought in tubes (which I then transfer to individual bags) I try to keep the item in the original packaging. I also keep invoices and a record of when and from where, whenever the item has a serial number. Does this matter really? Does it affect the resale price?
low premium is interesting, what is low premium can change, for instance, I brought some 10oz regal silver bars as low premium, but it turned out that only a small amount of those bars were produced before regal went under and now do command a premium. but things like buffs, or morgans or walking liberties or any of the "standard" low premium bars. that are produced in massive amounts, outside of scratching the heck out of it, or bashing it with a hammer .. wouldn't matter to me. but if it does for anyone, I'm more than happy to buy it off them at bargain basement prices. but with anything you paid a premium (above $1 or $2) for, you probably want to keep it in as new condition. as you are more likely to get it back when you sell it isn't damaged.
