Picasso Potrait Jacqulene, artist proof, signed in stone & pencil, dated 1960

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I am very interested in selling this which is on handmade black rag paper with certificate of authenticity from andrew weiss gallery along with picture of picasso & his daughter making print. Any suggestions on best way to sell? Also, galleries are not offering me what I paid for it.Any ideas? Why is it when they see an a/p on lower left corner do some people say it is after picasso? Any advice or help would be greatly appreciated. Thanks.