If you buy a bundle of games on GOG or Steam and you already own some of the games in the bundle, the cost of the games you own is automatically deducted from the total cost of the bundle.

Having the same system on Itch would be of great use to me since I tend to make bundles with all my games and this would allow people to keep buying my bundles (thus benefiting from the sale price) without having to re-pay for the games they already own from previous purchases.

I already made the same suggestion, so obviously I think this is a good idea!

Numerous times I've come across bundles I pass on because I already own one or more games in a bundle. It's not big deal if the bundle is already STEEPLY discounted, but if it's a %10 off bundle and I already own a game or two it basically costs extra