to be appalled at this leve of incomptency?

[SerenityNowAKABleh]

ARGH. As part of my job, I have to work with external vendors who provide us with information. I am in a rubbish position, as I'm the middle man between these vendors and some highly demanding end users.
One vendor has been harassing me for YEARS to use them, but haven't really. Finally, I decided to give them some work. So far they have:

1. taken ages to come back with a quote. And the quote wasn't even "£x, x number of days" it was a 12 page document. Nobody reads that, I don't need all that info
2. They then put confidential information in an email, after being told EXPLICITLY that this is a highly sensitive matter
3. I went back, said don't do that
4. They said, "okay, we won't".
5. Part way through, I needed an update. They put the WHOLE UPDATE in the email, with super-sensitive information in the subject matter
6. I went back again and said "don't do that".
7. I then asked for a final due date -they said 14th Jan.
8. They are now saying "tomorrow afternoon".

AIBU to a) think if you really want someone to use you, when given the opportunity, you provide a high standard of work and b) never use them ever again.

I'm thinking of drafting an email to the idiot who has been harassing me for three years about using them, stating exactly why I will never recommend them again.

Better to draw up a complete set or rules regarding communications (what medium, length of letters, scope and length of quotes, What may or may not be in an e-mail, what must be printed and sent, penalties for running past deadlines) and any other relevant factors beforehand, but not too late to send them rules now. Say you're sorry they seem to be unaware of your protocols, but this is the way business is done with your company, you're hoping the relationship will be productive for both parties, but it is to be done a certain way. Which is your way. End of. If they don't comply with the requests, end the business relationship on the grounds that they seem unable to perform as expected and requested. You'll have enough grounds to do it if they know what's expected.

Don't burn boats or bridges in business. Always try to look level headed. You have a job now, but you might end up applying there sometime in the future. Plus, handling conflict well/ solid and respectful communication skills is a good thing to have on your cv.