As a ex Esimator £2000 + materials used + how much rust and small dents cost, as a rough guide (rust under rear windows normally means new doors, secondhand good doors, or at least door skins) If bodged eg filled it will ALWAYS come back. You get what you pat for is the old saying and it is still very true. If you stick with companys that are insurance approved quality of work is usualy good with a garantee, but as with everything there is good and bad in both private repairers and insurance recomended repairers. Try for recomendations from friends or try someone recomended from this forum
Good luck