I would assume that you have a rationale as to why a user behind a proxy should be less trustworthy than another user not behind a proxy.

For example, in both my companys network and my home network, I have proxies that shield (if I chose to) my browsers from the direct contact with the outside - so I'm not sure, how much trust you should be putting into a recommendation given by a user from behind a proxy.

I see two possibilities of how to detect a proxy :

1. building a list of known IP adresses for big proxies (AOL proxies for example)
2. Looking at the X-Forwarded-For or the X-Client-IP header could also indicate, that this user is behind some proxy.

Personally, I would guess that "people behind a proxy" is a quite unsound criterion for "people much more likely to commit fraud", and you will most likely lose a part of your business (whatever it is you sell) due to it. Unless you have hard numbers on the part of your customers behind proxies and the number of fraudulent transactions, I wouldn't block proxies.

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
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