I thought they were selling sausages but they were just using them as a demonstration for engraved knives.
Do you want to buy an engraved knife?
No, I wanted to buy sausage, but now they're trying to sell me a knife and I don't want it.
It's unfortunate that you thought they were selling the sausages and they aren't but you shouldn't feel pressured to buy one of their engraved knives either. It's not something you want so you should just refuse the knife and leave the situation.
I just wasted 20 minutes.
I'm sorry that you wasted so much time, but there's really no reason to feel an obligation to buy an engraved knife if you don't want one. I think you should cut your losses and leave, and maybe try to find a place that sells sausage, so you can buy one.