Be sure to inspect the various stages of the work as it progresses and/or get them to send photos. Also discuss your concerns with your insurance assessor as early as possible in the repair process, especially about new verses old parts being used, panel replacement and bog thickness, as well as life time warranty. Only by being involved will you get some possibility of being well looked after.
But as mentioned, it’s usually paint that causes the most grief as some insurers are less than fussy with paint matching. However the standard is the vehicle must be returned to pre accident condition, so if there is any difference old to new paint, don’t accept it.