Since all exchanges in a market economy are voluntary, how do we know that the exchanges will probably benefit all participants

As bob is driving on an exit off the freeway, he comes to a stop light and sees a homeless man asking people for spare change. “see, he’s a perfect example of why we shouldn’t be giving welfare benefits to the homeless,” bob mutters to his wife. “he’s too lazy to get a job, but he’s healthy enough to beg people for their hard-earned money all day long.” what are the sample and the target in bob’s argument? are there any inductive fallacies present in bob’s reasoning (bias, hastiness, appeal to anecdotal evidence, self-selection)? if so, explain why. if not, explain why not.