Welcome to CSR Nation
Some agencies I work for let me charge extra for video, some don't. If I am already paying a scopist for full audio, why do they want even more for video? I don't think it is right. I am not that about "okay" being in there.
And also, almost every scopist I've used I've ever used goes too, too fast and that is why they miss so much. Same with proofers. They often go too fast.
Yes, I think they just go through editing/scoping too fast, not paying close enough attention. Or don't even listen to every word. I've seen good proofreaders miss too much because they are reading too fast.
If I get paid more, I pay the scopist more. By the same token, I expect them to work with me on price when I'm not being paid more.
I tend to cut them some slack when it comes to scoping videos. We hear while editing. They read while editing. I expect them to miss some things.... not a lot of things, but some.