The most important aspect is, make sure the engine oil is genuine and not the recycled one.
Nowadays, lots of recycled engine oil sell at spare parts shops. Normally, they sell it slightly cheaper from the oil manufacturer recommended price. Make sure you purchase it from "trusted" shop, or if you are not sure which shop, just buy from the pump stations.
On the other note, I know some of forumers here have heard about staffs of some authorised car service centres (cannot revealed the name cos no proof) doing some "project" regarding the engine oil. The modus operandi is, the changed the engine oil of the customers' cars with genuine engine oil. As we all know, most engine oil bottled in 1L and 4L packs. Let say the car needs 3.8L for engine oil, they will pour the oil in exact quantity into the engine, but they will keep the balance of 200ml and charge customer based on 4L price. This balance of oil (200ml) will be use for the next customer (let say also need 3.8L oil), and will have a new balance of 400ml. The will do it over and over again for the next customers until they get "balance" of exactly 4L in an unopened bottle. The staff will sell it outside with a very attractive price.
I knew this "project" through my friend who sold me a bottle of unopened 4L Syntium 3000 fully synthetic printed with Pr#&on logo with a price of RM 50.00
Now, I regret already. It's not that he cheated me with the fake oil. For me, it just unethical attitude. Now, I stop purchasing engine oil from him (even though it's very hard to resist the temptations to get good things at cheap price). The worst part, he mentioned to me that this "project" is normal and happens at any authorised service centres and some of them even mix the fresh engine oil with used engine oil into the customer car, to speed up the quantity of unopened bottle of engine oil.
My advise to all, if you change your car engine oil at any authorised service centre/dealer, please ask the balance of oil. You have paid for it, so you deserved to get the remaining/balance of the engine oil.