If I want to know how much something goes for when I sell it, I'll check 'completed items' on eBay and go from there. Values are point in time... especially for Transformers.
I may be mistaken but I thought that the graph pulled its info from 'completed items' .
I'm currently building a small inventory to make a little extra cash off of ebay so I am a bargain shopper. I often look at that graph (because I thought the info came from completed listings) to determine weather or not I will make any money off an item. I consider shipping and packaging materials when doing this as well as ebay's 8%-9%. If I can make $0.50 or more by offering SMRP+shipping I buy it. If not I pass.
I enjoy the hunt and am shopping for my collection anyway, so that part in and of itself isn't putting me out so I'm not in it to take advantage of people. I really want to be a 'For Collectors by a Collector' kind of situation. I want people to be able to have and love these items because I have and love them. It's not the next big e business by any means but I often seem to be able to find my items at 40% off MSRP or more so buy buying them at that price now, I can sell them at MSRP-ish and make a small profit. (I say -ish because deluxes used to be $10 now they are $15 so i'd make some coin on that alone.)
For example, I've seen some good prices on Generations Kup and Warpath but they don't seem to be selling that well or for enough on ebay for me to pick them up so I've passed on them. (Which honestly surprises me because I personally love them toys) But I check every time I'm out so if I see the trend changing, I'll pick them up for more of a quick flip. (BTW if anyone needs one of those PM me and I may be able to work something out if you're willing to cover shipping costs.) (Side note. My Gen Kup's head is really loose so I can't guarantee that won't be the case with a NOC one.)
There are a few things I've picked up that I won't even try selling for a while because I know they seem to be hard to find as well as seem quite popular. So in 6m-1y or more, when it's even harder to find them on ebay, I'll sell them for a small markup, just because at that point they become more of a collectible than a retail product. But most I plan on putting up in a few weeks or a month. Right about the time they seem to be hard to find at retail.
Then there are some items that will almost certainly be highly collectible down the line. I plan on making this a supplemental hobby along side my personal collecting.
Like any investment you have to keep your eye on the market.
When I'm ready to start listing I'll start a thread. I will also set my links up so that they will appear to come from this site so shmax.com will get a cut of any of my items not found directly on ebay. So I'll be helping the site out as well. It doesn't come out of my profits so why not? :-)