is this seller's autographed posters/items legit?

[CloverClover]

I might make an offer on this guy's heat poster, signed by deniro and pacino, but I don't want to get scammed, here is his ebay list:

http://myworld.ebay.com/authentigraphs-ink/

It says on the item:

"You are bidding on an Autographed Poster. It is NOT a pre print or a copy.

This is the real deal!!!

This Item Has been Authenticated By PSA/DNA.

PSA/DNA is the Top Third Party Authenticator and is Ebay’s Pre Approved Authenticator.

This poster will include
a PSA/DNA Certificate of Authenticity with MATCHING numbers on the COA and photo!!"

But how can PSA/DNA really know what is legit or not. What are the rules for getting signed items?

[DvDDan]

if it has the certificate with it and you can verify it before buying i say go for it

[pilot]

Check out PSA/DNA's FAQ: http://www.psadna.com/faq.chtml

[CloverClover]

The only problem is they put a sticker on the items which says PSA DNA and a number. Do you thikn this might make the item less valuable? I dont see why a collector would want a sticker on their original item

[Cheato]

Similarly, I don't see why anyone would pay anything for a signature. But some people apparently do that. Every collector has his/her own set of standards.

[jjcool]

While I think it would be cool to have some of those items, their pricing seems to be higher than I would be willing to spend.