Air tasker has a lot of bad reviews on trustpilot. Why is that?? Probably scam?

Depends on the people you do a job for or have a job done for you. A lot of people get picked because they are cheap and don't do their due diligence. Airtasker actually has badges associated with how trustworthy a person is, look at comments left by people who have used them before etc.... However instead of taking the time to get rid of the trash on airtasker, they just bag airtasker as a whole. In Australia we have another site we use and usually compare between the two sites when we need a job done to get the best person and price for the job.