[Amazon] Sonic CD - For free (No steam key)

I don't think you tried hard enough. :P

?tag=xxxxx is for profit purposes.
Any other strange stuff on the end of an Amazon link is for tracking type stuff though.

Just checked epicbundle.com, and it seems everything is loaded with referral links so they can make money.

The Amazon links all have ?tag=xxxx
And most of the other links use "commission junction" (the ones that start with tkqlhce.com / dpbolvw.net / jdoqocy.com /etc...)

Yes it is. On Amazon ?tag=xxxx is a referral link that earns the person that 'owns' the ?tag money.