I'm interested to buy some artwork / photogrpahs online from some
artists /  photographers and they have mentioned in their web site
that their photos are at limited edition and come with the certificate
of authenticity. My questions are: 

1. How can I ensure that the artists / photographers are honest about
the number of copies he is going to make ? If he state that his work
of that picture is limited to 100 pieces and will be sold worldwide,
how can I know he does not sell out 200 pieces instead ?

2. Can the artist / photographer issue the certificate of authenticity
by themselves or they have to register or declare their work with
someone else for witness or control purpose ?

3. Are there any 3rd party companies or organization providing
trustworthy service to warrant and manage the artist's /
photographer's  work in selling limited copies of their work ?

Thank you,

happychiru