The affidavit of support (I-134) is not legally binding on the sponsor so the government cannot sue you and neither can the person who is listed in the form if you do not support them. I-864 is legally binding however the law does not allow DV applicants to utilise this form. This information is widely available. When you ask someone to fill it out, tell them its not legally binding (as per the US dept of state foreign affairs manual which consular officers use)
"a. With the required use of Form I-864, Affidavit of Support Under Section
213A of the Act, under INA 212(a)(4)© and INA 213A for so many
classes of immigrants, the use of Form I-134, Affidavit of Support, has
been reduced considerably. Nevertheless, there still are circumstances
when Form I-134 will be beneficial. This affidavit, submitted by the
applicant at your request,
is not legally binding on the sponsor and should
not be accorded the same weight as Form I-864. Form I-134 should be
given consideration as one form of evidence, however, in conjunction with
the other forms of evidence mentioned below."
The above was taken from the U.S. Department of State Foreign Affairs Manual Volume 9 - Visas - relevant info from page 13 to 15
http://foia.state.gov/masterdocs/09fam/0940041N.pdf