How do we sort & value a construction toy collection?

I've found that Facebook has groups dedicated to most types of collectibles. I've found great advice and information there.

Most of the value in collectibles lies not in the raw material but in the labour involved in researching prices, assessing condition, photographing and listing on-line or otherwise making them easily available to purchase from a trusted vendor, etc. Unless somebody wants to temporarily re-purpose themselves into a dealer of these things, I'd look around for local dealers of such things, and solicit offers. EBay lets you view completed listings -- where you can see what things actually sold for -- use that to assess retail value; asking prices for items not yet sold are largely meaningless. But if you use this as a metric for the value of the collection to a dealer, remember that there is quite a lot of work between "sells for $X" and actually completing a sale for $X. You will be offered a relatively small percentage of X. You would want to ID all the items -- year of manufacture, name given by the manufacturer to that particular item, basic description, and notes on any damage/wear (be picky; collectors are very picky). If anything has the original box it came with or even a pamphlet that came in the box, that's a thing to note. Collector-specific forums would be a good place to make inquiries to dealers, and possible sales -- still with the caveat that selling involves a lot of labour; this will be many hours of work with all the risk on your end (for example, when you sell X and are not familiar with X yourself, you may overlook important things about condition etc, and end up with irate buyers) rather than your friend's if you undertake it yourself.