Muhammad Ali over Liston - real autograph or not???

Hi,

I have never purchased any sporting memorabillia in my life and I
really want to buy the Muhammad Ali over Liston signed photo....I have
seen many 16"x20" around in the shops and on the internet.

I have had a look at the Certificates of Authenticity that are
provided with them and all the certificates appear to be nothing
special (very easily forged)...I have also seen it at varying prices
$200 - $1000.

Can anyone please let me know how I can be assured that I am buying
one that was actually signed by Muhammad Ali? I am very scared of
getting ripped off as it costs a lot of money.

Thanks in advance for all your help!!!

Kindest Regards,
Ruslan.