1921 Registered Turkish

I thought this was a interesting item, how do dealers price these things anyhow?

A beautiful piece Brian. Thanks for sharing it. I collect overprints but have not seen these stamps before.

Some stamp catalogues have a price for stamps on-cover. I would assume (but am happy to be corrected) that some dealers add the on-cover values together. Others charge a set amount such as $1 or $2 each; these are the ones I look through which probably explains why I haven't seen these stamps before.

Fantastic cover and great question Bryan. To me, there are a number of factors that influence the value of the cover: the stamps, cancellations, auxilliary markings, denomination/usage and aesthetics.

A dealer asks himself a series of questions:

Is the stamp(s) rare, of fine quality?
Is the cancellation well placed and legible?
Is the cancellation of special design, or from a special event or place?
Are there auxilliary markings (such as a blue cross on the front in drawn in pencil, or a "date received" stamp or registered stamp)?
Was this stamp normally used to send this class of mail (try finding a piece of US mail with one 14 cent stamp on it)?
Does it look good (envelope in good condition, clean, carefully opened, etc).
A dealer might also examine the cover to see if the envelope, stamp and cancellations are fitting and appropriate for something of that time period (checking for cover forgeries).

Thanks for looking guys and the answers!