Do not use appearance as the only test
A shallow dent does not tell you everything about the assembly. Describe where the bumper made contact and whether the door was open or closed. Avoid cycling the door to prove it still works if sections, tracks or hardware look displaced.
Record what is visible from a safe distance
A general photo can show the affected section and the overall opening. There is no need to remove covers, reach between panels or stand beneath an unstable door. Explain if the opening must be secured or if a vehicle remains trapped inside.
Compare the assessed repair options
Ask whether the section can be addressed on its own and how a replacement would match the existing door. If broader replacement is proposed, request the reason. Keep cosmetic appearance, structural condition and operation as separate parts of the decision.
Your questions
Does a dent always require a whole new door?
No universal rule follows from the dent alone. The condition of the section, available replacements and the rest of the assembly influence the options.
Can I push the panel back into shape?
Do not attempt to reshape or reposition a damaged door while it is installed. Have the assembly assessed before applying force to it.