How to scan if a user has a dymanic IP address, or say they are too small to have a fixed IP?

How do customers handle scanning them multiple times?

On the basis that their Ip may change even during a scan, does the penetrator support dynamic DNS somehow?

Most easy is if they put in the entire c class
example 192.168.1.0/24

and one day you have 10 systems active
next day 20
next day 18

Then it will report on all found.

It's possible that client computers change their IP, but it's more likely that the dhcp server assigns them the same IP as the day before, depending on the lease time defined on the dhcp server. Whenever possible the hostname should be used instead of the IP address, however it's more frequent that customers want to scan server machines, which are usually configured with static IPs or are always on, rather than clients.

In any case, yes, it's possible that a scanned machine changes its IP address and the day after it cannot be recognized any more.