Note that “unusual and not documented” does not mean “wrong” - many should be simply documented.
Some may be fixable remotely:
clear typos (shop=suupermarket)
written in language other than English but with clear mapping to local language (for example shop selling meat in Polish is “mięsny”, so shop=mięsny is clearly shop=butcher)
too specialized tags (shop=coal is better tagged as shop=fuel fuel=coal, shop=office_furniture as shop=furniture furniture=office, shop=indian_spices as shop=spicescuisine=indian)
very clear duplicates (shop=hypermarket vs shop=supermarket)
shop with website, maybe even linked in OSM object, that allows establishing proper value of shop tag - it is also worth adding website tag
in some cases something is clearly not a shop (shop=factory_producing_widgets is likely man_made=works)
needed and valid shop value that should be documented at OSM wiki
Some may require resurvey, if one is luckily in your area you can check it. Or you can create a note and wait for local mapper to resurvey it.
Contacting original mapper may make sense.
Remember, it is better to not edit than break data in case of tagflidling - create note if unclear or unsure.
Let me know if this list is useful but outdated (I will setup refreshing it in such case) or pointless/problematic (I can delete it if it is causing more problems than benefits).
Some improvements can be made to this list… Mayvbe mark cases with nearby notes opened already so these can be skipped for now? And mark cases where website link is available so these can be processed first?
Cases on "entries from list of suspicious ones: " list can get explanations why this values are treated as invalid. Maybe more.
(helping here is useful as it allows to reduce number of not needed and pointless top-level shop values, on 2023-08-14 we had 11 215 distinct shop values, vast majority bogus, broken or not needed. Reviewing such lists also allows us to spot missing shop values, problems with documentation and presets. Repeated appearance of shop value may indicate that wiki or presets should be improved. Maybe iD translation is bad or requires additional aliases for easier search? Maybe OSM wiki would benefit from translating it to local language or being more clear?)
(I can also generate such listing for other areas, let me know if someone is interested)
On the JOSM link, yes with that overpass query you can download all unusual shop values but what I meant was a link like for instance also Osmose provides as (j)
Bear in mind that unusual does not necessarily mean wrong. shop=* is an open-ended tag-value set, and user-defined values are explicitly allowed.
If a value seems odd, a documented alternative exists, and that value corresponds to the actual shop’s type: go ahead and change it. But please don’t change values for the sake of getting rid of rare ones.