Kobo has stopped offering price matches for Kindle books that are "discounted" -- those that have a red percentage next to the price, and a crossed out "Digital List Price".
I asked Customer Service if they'll accept a similar price discount on Google Play's book store, and they said yes, but I haven't tried it yet.
Reddit thread:
https://www.reddit.com/r/kobo/commen..._not_reliable/
The rule of thumb is not to download the book until the price match is approved, to allow you to ask for a refund.