Safest Place to Buy PC Game Keys

Hi,

Besides Steam, what is the safest place to buy PC game keys? In my journey to find a cheap copy of Sonic All-stars Racing Transformed for Steam, I've ran into G2A and Kinguin. Are these sites safe? Has anyone purchased keys from sites like these. I've used Green Man Gaming once but the process was convoluted.

Please help.

I didn't find the right solution from the Internet.

References
gbatemp.net/threads/safest-place-to-buy-pc-game-keys.486458/
Cloud overview video

Thanks