not sure what the difficulty is with photographing tightly rolled posters. I do it all the time and without having to 'flatten' them in any process.
It's called "I use magnets and my photography table has a sheet metal back so the magnets stay down"
but length of period.. 4 months is far too long for a consignor to wait to see their material sold.
Generally speaking, when people are looking to sell, they're looking to sell in a compressed time frame. Also, what the value of a consignment or of it's individual posters are, once you take them, you do expect to have to deal with them, especially when you are a large company as opposed to my one-man-army.
Obviously, if it takes 4 months before you see your posters for sale, maybe the issue is about a seller having 'more than they can handle' with too many consignments, or maybe you as an individual are just not important enough for them to pay attention too.
I have my own experience with a box of top quality stills not even being opened for 6 months and part of my consignment being mixed up with another consignor's material. (you can actually find my tale posted in the Mopo archives)
That said, when you send your consignment to someone, you have to be willing to accept the vagaries of the business and of course, the old adage 'patience is a virtue' clearly rings true
there are a couple other comments though. 1) if you accept a consignment, whether you are going to make $25 or $3.75, you have no complaint about it. Just like the guy who wonders why it's taking so long, you accepted it and have to live with it - even for $3.75 .. and 2) "Please post your name so I can post exactly what you sent and why we have not auctioned it yet. And if you prefer not to wait, I will return them to you right away, so YOU can send them to another auction company, if you can find one that will take them." is never a way to speak at a client unless you plan on telling them to screw off
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Moving passed that, my suggestion is you try to sell them on ebay or Craigslist. There is a variety of ways to post them and they depend on how much time you wish to involve yourself with. It sounds to me that you don't want to spend very much time, so I would make up lots of 50 or 100 (50 may be best) and list them. Give as much information as you can (like a list) and a couple pictures of the best posters in each lot as well as a picture of the roll itself. You may wish to restrict sales to the USA, as 50 posters weigh approx 12-14 pounds and shipping them overseas will cost hella money.
or for Craigslist, just advertise the entire lot, for one price, with pick-up only
if you plan on selling them yourself, in lots, I recommend calling Uline
https://www.uline.com/ and either order a case of 36x4 inch tubes
https://www.uline.com/Product/Detail/S-3573/Tubes/Kraft-Mailing-Tubes-with-End-Caps-4-x-36-080-thickor this 28x4x4 box
https://www.uline.com/Product/Detail/S-4577/Corrugated-Boxes-200-Test/4-x-4-x-28-Tall-Corrugated-Boxesyou may choose the box, as for a non-usual seller, it may be easier to deal with.
use some brown kraft paper to wrap the posters before you package them and fold the ends of the paper over the ends of the poster roll to prevent what damage you can and use some peanuts or bubble wrap at the ends to fill the box & for added end protection
after you've done all that successfully, let me know, I have 250,000 posters I'm trying to sell, including bulk lots.. I could use a little help.....