And i ask myself if its ok when i pay out 95% of the paid bitcoins at the end so that i dont have to sit alone on the accrued costs and the work time.
The way I see it, the chips cost BTC 0.07821 per chip from Avalon and we paid you an extra BTC 0.00779 for the service of organising the group buy.
If the refund from YiFu is BTC 0.07821 then naturally that should be refunded to buyers. If you choose to choose to refund a portion of the BTC 0.00779 then I'm sure people would thank you, but it seems to me you've done a lot of work and you're certainly not obliged to return all of it (or even any of it).
Just my 2c - I haven't decided if I'm going for a refund yet or will just take the chips.
roy