Tell them to clean the compacted lint out of the port using a straightened paperclip. Due to the nature of the lightning connector design the wedge-shaped connector can push and compress pocket lint into the port until enough is there to prevent a clean connection. This is a valid complaint about lightning connectors, with a solid center it can compress this lint while the internal post and center connection point of usb-c makes this less of an issue. OTOH 'springs' wearing out or other worn parts on the iPhone side of the connection that require replacement are a non-issue.