Not sure if I am allowed to give anything for free
The idea would be to reward short-term buyers with a giveaway

V Idea
Giveaway:
Every buyer in the next 48 hours will be eligible to win a free Pul Rune.
All buyers will have their usernames placed in a list and list will be sorted out at [random . org] at the end of the giveaway period.
#1 of the list will be the winner.
Results will be posted here.

Am I allowed at all to do this??

I don't see why not. As long as they're not paying directly for a chance at winning. This has to be secondary to your sales.

This is not allowed and considered as Spam.
If you want to share your wealth, simply post a game & password in the desired section ( need to be as service ).

if you have questions, feel free to pm me.