OEM drives are simply regular drives sans the retail packaging. DVD burners are frankly never intended to be sold retail, and 90% are OEM. Only a small percentage of drives are dressed up specifically for the retail market. In other words, OEM is what is normal, and it’s retail that is a deviation from that.
Tech retailers such as NewEgg, ZipZoomFly, and Fry’s Electronics get their drives new, direct from the manufacturers. Many of these drives are not sold in retail versions, and can only be bought as OEM. Also, most of the OEM drives are available before any retail versions show up in other kinds of stores. Once again, DVD burners are considered to be first and foremost an item to be installed by system builders and technicians, and that is the way they are originally handled. Retail boxed products, especially those from companies like Lite-On, are an afterthought.
As for keeping them separate from boxed drives or returns, NewEgg and other sources of OEM drives have quite modern facilities and procedures for handling that kind of segregation. The people here on CDFreaks can tell if something has been used, and our experience is that it happens very rarely. More importantly, places like NewEgg have great policies that will correct any mistakes ASAP.
If you’re going to be paranoid about it, you should stick to buying retail boxed drives. OEM is the only way you’re going to have access to the latest and best though.
As for the specific deals you posted, the drives are OK, but not the best, and the prices have been lower many times before, so unless someone needs a drive now, they should pass and wait for another sale. I would suggest the Lite-On 20A4H over both of the above drives, although the Philips is a rebadged Lite-On 20A1P, and it’s also a good drive, but not as good as the 20A4H. The Samsung is a poor imitation of it’s SATA cousin, the 203N, and many folks who have tried it are disappointed.