Inspired by Tamarind's latest post.
What the fuck do you want!?
They don't know.
They really don't, and that's the whole problem. They are using you as a crap version of wowhead, a tool for searching for enchants.
So just link your book and what's the problem? They can't even search wowhead. How likely are they to be able to successfully figure out which slots don't have enchants, find the enchants they want for those slots, get mats, bring them to you, and do all that before you notice that you've been standing around Dalaran for the past half hour as they have 5 minutes left on their hearthstone and you are not queued for a random or BG, not in a raid forming, not making gold at the AH, and not farming?
They won't go away if you ignore them (not /ignore, just nonresponsive), but they won't waste half an hour of your time as they slowly figure out what they are doing. And then get invited to a raid right as they are about to open trade and hand over what might actually be the correct mats. Yes, they have been busy finding a raid to carry their enchanted selves while you've been patiently waiting, hoping for a 5g tip for a half-dozen enchants.
I am not a pessimist!
A pessimist wouldn't know about scrolls. For a mere 1-4g you can put an enchant on a scroll and never have to deal with this ever again. They don't even have a deposit. You will lose the AH cut, but with proper pricing you'll make far more than you'd get from 5g for half an hour.
"LF Enchanter to do X, have mats"
Shift-click that person and if they're in the same city, go get some gold. This person knows what he wants and knows how to get it.