Thank you sales. I'd also have some other ideas which may pertain to a commercial cooperation for the site. Where can one get in touch?

The idea above gives a health rating for your collections. Since I collect across platforms I see the system being usable for almost any type. Even cassettebased ones. However, I did forget to bring a particular status, which is that of the box. 
Ie. G+ cartridge in a A box. In my offline tracker I even included if carts have batteries, or special statuses for things that contain consumables (mostly meaning batteries).

Id rather do most things in PC than in parts online, parts excel.
Today I print out the excel with the grading field and battery field indicated to achive ultraspeed browsing at flea markets etc.

Using the lot value calculator or any variant. 
https://www.pricecharting.com/lot/5wkxpvznkp

There should be a toggle to switch between if the game is loose, CIB or new, and when toggled updated with price relavant to current state of selection.

Correlated with what we want to know. Do we have this game from before? And preferably, what state.
So I pick Banjo-Kazooie and get the price CIB as that is what is for sale.
I see I have BK from before, and if it is CIB or box+game. 

Last bit is more tricky, as it relates to personal evaluations.
But over time it should even out.

I have started to enter what state my games are in.
B - for bad (usually includes notes)
A - for average 
G - for good (no deep marks, 
VG - for very good (which would mean (almost) flawless to my knowledge.

I also use - and + as modifiers to indicate whether or not it's up there. 

Example: If I see a G item, particulary G+, I don't bother to replace the one I have or match them to see which is best.
Then only a VG item will be used to replace the current items place in my collection.
Saving a lot of wear and tear on taking things in and out of boxes and covers.

In addition, if used extensively, the system could add on an opportunity to upload pictures of my own items.
Haven't worked out a common system yet, but I would say Im using an 850lm Ikea E27 bulb at a distance of 4-6 inches to evaluate my items. Moving the item allows me to see how the item has flaws and how deep. 

This system will not replace grading companies, but to a certain degree it will reduce the need for them on lowerend items.
The last bit is that the average evaluation of ALL my items would give an average of my ratings. Lets say my average rating would then be 74%. (I can provide my math on how to get to 74%). The sum of ALL evaluations might be at 68% or 82%. That would give a me prompt to reevaluate my evaluations of my own items. A button provided which states, Certify quality evaluation (and if checked, gives higher relevance on my collections in the average based on the size of that collection).

So I check - Certify, My collection now has a 3x the relevance in the averages.
I have to recertify every month or two. (Easy update, just with another overview on my collection vs the average).

Quantified this would give AWESOME indications on how well the state of your collection is.

Later we might have second-verification if an item is sold between two users on this site.
(Like chess-elo ratings) giving certain users a higher relevance based on how well they hit.
 
Heck, it might even be a thirdparty opportunity here to mediate this for a small fee. Not as a decision, but to make parties reach a common ground.