at the top of each game page and dev page there should be a red flag section:

-if a purchasable game has no download

-if a game has released on steam but the dev never followed through on providing steam keys in cases where steam keys were part of a game purchase

-if a dev has deleted the download page for a game they have sold so customers can no longer download it

i would like to think this would make devs more honest, but will settle for protecting people from being scammed

on point one and three the problem is a dev can delete the download file and download page and itch doesn't seem to keep a backup to roll back to, not talking about them removing just the store page for a project they wish to abandon. it breaks the "and have offline access to it forever" thing you mentioned, yes i have done the recovery of purchase download links through email and several projects deleted the DL page, more simply don't have the DL file(s) anymore.

on the steam key thing that is why i specifically mentioned it only applying when it was included in the purchase, most easily where they checked the right box so the store page and dl page note the purchase includes a steam key; this is easiest to check since the dl page will have "your purchase includes a steam key" but there won't be any keys for the box to dispense

 possibly also where the dev specifically promises keys to be included with a purchase or above a certain purchase amount though i would expect less enforcement of that with how easily a dev can delete the store page and thereby the easiest documentation of such a promise

on why,  partially principal since it was part of a purchase, partially because some devs stop updating the itch version after getting on to steam, partially because it is insurance if the dev deletes the project on itch or if itch ever goes the way of desura (lost a lot when they went down)

on language that's why i chose the term "red flag" which is appropriate even in situations where they've tried but failed to complete a project, the word scammer is appropriate in cases such as where they delete a download, delete other files included at higher tiers, or don't follow through with explicitly sold keys. 

All of the scenarios i mentioned are where users would have no option to get what they paid for, at least seemingly, it would be useful if the 

"This project is not available for download

This game is not published and can no longer be downloaded." 

page had a simple one button report thing to simplify and automate itch checking if they have a roll back, or if a dev emptying a dl page without putting a new file in a reasonable amount of time would trigger a potential problem flag, on the steam keys the easiest way would be if the steam key box had a button that would open a box where you could put a steam store page link so support could quickly verify there was a steam release without follow through. non-automated support should be a last resort

 "keep a local copy..." lots of problems with that, not updated, need a huge server farm, and people would spend all their time trying to manually update and organize a collection without ever playing anything, back when  i used to fill hd with stuff like that and make database sheets of which pc gamer disc had which patch for which game, etc.  sounds simple, becomes insane

While I am not opposed to the idea of more accountability, the more complex the solution, the more I see the potential for abuse as well as additional strain on a small team that’s already overwhelmed with questions, complaints, feature requests, claims (false or genuine), reports, as well as people that “have to be kidding me” as it is.

What’s more, I think a developer is legally able to remove their project from a site that hosts/sells it at pretty much any point. I wouldn’t expect that itch has any legal ground to just reupload previously uploaded content without the consent of the developer/publisher.

And the term “Red Flags” would likely drive business away from itch to less scrupulous sites.

But some things seem doable:

• The number of paid projects that a developer either removed the installers or store page for should be visibly displayed next to their name (“Galaxy_Tech (1 withdrawn project)”) - with a little mouse_over text that explains what that means in detail. People can form their own opinion if that was just housekeeping or a foul move.
• Personally I don’t use Steam, but the issue with the nonexistent Steam keys definitely sounds automatable.

Developers that stop updating their game after getting it to steam is not a problem on itch alone. While morally, the fault lies with those developers, users should feel obliged to use tools like comments, reviews and ratings (both on Steam as well as here) to inform others of shady business practices. But most importantly: They should think twice and look at some reviews before they even consider buying an unfinished product. There’s no need to pre-order a digitally distributed video game, but if they want to support a project that’s still in development they always do so at their own financial and emotional risk. If people don’t use some critical thinking on their own, nothing we can say or do will be able to save them from themselves.

As for managing local copies of digitally distributed games, I download the installers for the games I own* and keep them on an external HDD. Like you said: It’s tedious for games that still receive updates, but it’s a solution that works. I, too, have too many games that I don’t find the time to play. But at some point I stopped buying games that “looked interesting” just because they went on sale and restricted myself to buying games I really want to play right now. (I’m looking forward to Hades coming to itch.)

.* When I write “games I own”, it does not include about 98% of the things from the Bundle for Racial Justice and Equality. I’m only human… ó.ò

not only is that not how steam handles removed games there is even a removed game collector club over there

https://steamcommunity.com/groups/RemGC

google and apple however i can't speak for