If undesirable people are filling out your web forms, like form spammers, you should block them. Of course you could block their I.P. address from visiting your web site altogether in the first place. Contact your hosting company for help with setting that up. Additionally, you can block their email address and/or their I.P. address inside your 1Shoppingcart account.
First login to 1shop, and click on "Contacts" then "Manage Contacts". Search for the person who you wish to block. Once you've opened up their full contact record, you'll see the option for blocking their email address from submitting any new forms to you.
Also, on the details tab, you'll see their I.P. address and you have the option to block that as well.