My RC currently reads as follows:

"I prefer hardbacks with dust covers included - if you are sending a hardcover book which originally came with a dust jacket, and no longer have the dust jacket, please reject my request. Thanks!"

I just got a rejection from someone who gave the reason as "my book is a paperback." Huh??? Something similar happened with another recent request, although that person chose to accept and then PM me just to make sure I didn't care that a mass market paperback had no dust jacket. (Sigh.)

I suppose they might be misreading my first phrase "I prefer hardbacks with dust covers" as "I prefer hardbacks" full stop. Should I just remove everything before the hyphen, or should I just accept that sometimes I'll get someone who doesn't read RCs very carefully?

(BTW, I've gone back and re-requested with my RC turned off; hopefully that won't confuse them that much...)

Start with, "IF" I have requested a hardback ; I only  want it with its' dust jacket.

                   "IF " I have requested a paperback  of course I know there is no dust jacket

What Fara said; I know the Help Center uses "prefer" in their examples, but it isn't a definitive term. 

And folks will always wonder about the binding types you don't mention, so what to do with paperbacks is a good inclusion.

Since it has happened twice, I'd change your RC to be super specific:

"If I have requested a paperback, please send it as I have no conditions for them other than postable condition.

If you are sending a hardcover book which originally came with a dust jacket, and no longer have the dust jacket, please reject my request. Thanks!"

The wording is ok, but seems a bit...stumbling. How about something like:

If I ordered a book listed as a paperback in the system, I have no additional conditions please send it.

If I ordered a book listed as a Hard Cover that originally came with a dustjacket, please include the dust jacket. If the dust jacket is no longer present, please deny this request.

Here's another wording idea for you to kick around:

If this book is a paperback, please send the book like normal. 

If this book is a hardcover please include the dust jacket if it originally came with one.  If no dust jacket, please deny this request.

I used to get the same response when I had my former RC. Could never understand why they would reject it with "It's a paperback." I know it's a paperback. lol

I changed it to this and haven't had that problem since:

* If this book is a hardcover book, please include its dustjacket.

* If this book is a paperback book, please ignore this RC and send it.

This is mine, which is pretty successful, I added the line about the paperback when I started getting the declines because "this is a paperback".

If the book is hardcover, I would like it to have the dustjacket. If the dustjacket is old, worn, or torn, this is OK.

If the book is a hardcover and has an illustrated cover but not a dustjacket, this is OK.

If the book is paperback, I have no special conditions.

Thanks very much!

Ditto what the above people have said.  I find that putting the paperback first saced me a lot of trouble.

The RC's I use:

PLEASE, ABSOLUTELY NO BOOKCROSSING BOOKS!!!

If this book is a paperback, it must be in good condition as required by PBS.  The rest of this does not apply.

If this book is a hardcover: it MUST have the dustcover.  Library plastic over the cover is OK.

Library copies are OK.  In fact, I prefer library hardcovers for my collection.

Or you could just turn your RC off when you request paperbacks.  Some people turn down any and all rcs (which is their right) and the reason they fill in might not be the real reason they turned you down.  Instead of saying "I don't do any RCs ever" they might just put in "it's a paperback" because they don 't want flack for turning down all RCS. 

What Mary said..

This is what my RC is too, and I ONLY turn it on when I've requested a hardcover. Paperbacks are on auto on my WL, and HCs are not.

I've also had a problem with a similar RC. Mine used to just state "If the book I ordered is a hardcover, please decline if the dust jacket is not included." I can't tell you how many people turned me down with "this is a paperback." The word "if" just seems to be beyond some people. I have since prefaced my RC with "If the book I ordered is a paperback, please send it." I've had no problems since I added it.