I can’t see dropping $300 at once, but I use Google Play extensively. I use it for all of my movie purchasing needs, and you can also subscribe to various streaming services through Google Play… If I could justify the instant expense I would take them off your hands!
when i made the mistake of looking for a personal online i had dozen of calls that would go through the whole song and dance giving me any amount thAT I WANTED and then get told "well to verify your identity go to walgreens rite-aid ect and buy 3-500 dollars of various branded gift cards "
and they’d use legit loan places and use their name in the phone call… iiits so bad that one of the few legit loan places has a recorded disclaimer "we do not give loaned that’s less than 1500 and bore than 5,000 nor do we accept gift cards as identity verification " If you get a call from someone using our name it is a scam and and notify the applicable state attorney generals office and even them i had people say “well what if its not a scam …”
sorry about the typos but I had a call and missed the editing timer…
Typos: I thought you were mimicking the bad grammar etc. frequently used by scammers!! 
To the OP: yeah, if the cards are good, then your best bet is to ask around your friends etc. to see if anyone can use them. Maybe offer at a slight discount, comparable to what Costco etc offer.
I get some Play Store credits through an app on my phone, and I use them for the occasional movie rental or in-game purchase. You may not personally watch 300 dollars worth of movies, and I would personally not buy ebooks from Google unless I was sure I could de-DRM them (platform-proofing).
Thanks to all for the helpful info- I will let you know how it goes!
This place is a gold mine.