Maybe we should also update it with avg prices for used items. though updating it is a humongous task. often have seen 35mm 1.8g dx people wanting to sell it for 300 +- 10$. It looks like after they use the lens for a year or more the lens gets star status that it was used by celebrity x before so the value has gone up more than a brand new one with warranty. then there are those that change system but still will put a buy request for the same system that they are selling. Lens in mint condition but has a few squeaky sounds, and has a few user marks - IS not MINT.
new buyers :
If there is an offer that you see someone selling something that you want then
a) Check the price of a new one first
b) check the price from other users on BnS
c) check the users post for how many times they have posted/reposted the item. ( when you combine points b and c it will give you a close representation of whats selling or whats not at their asking price)
d) If the item is out of warranty then check for new items - gray set ( they are sometimes cheaper than used items posted in BnS)
e) be care full of poster who are new and have few post counts as well. ( they could be the same people who are not getting their stuff sold so they create a new identity just to avoid questions that they maybe asked as to why the items have not sold for so long)
Don't be finicky about boxes unless you are collector and not a user of your goods. ( boxes can be had from ebay for around 20$, and that no excuse for a seller to sell the item for 100$ more just coz it has a box, maybe for a lens under warranty it gives a psychological advantage that you are buying a new item, as well as if its less than a month old it can be returned for a new one if you have the entire package, else they will repair for you and in any case never ask you for the box.
Some points mentioned above, people may have their own views and i respect that, i am just airing my views if some thing is very different then let me know and ill update this post.
Peace.