‘My Jewish friend is in business of importing non kosher wine from France. He has found a deal to buy, but he is short in capital. he has asked me to invest in this deal, with 20% return. He is not shomer Shabbat and his business is open on Shabbat. Can I invest in this deal? or just lend him the money with no interest?
If he’s offering a 20 percent return, it follows that the arrangement is not an investment but rather a loan on interest. Therefore, the question is whether or not it it permitted to lend a Jew money for the express purpose of doing something prohibited (such as dealing in non kosher wine).
If you know that the money you are giving your friend will be used for non-permitted purposes – such as the deal you mention in the question (it is not permitted to deal in non-kosher foods) – then lending him the money will be a case of lifnei iver. By lending the money you are making the deal possible, and this is not permitted.