On some Flippa listings, you'll notice a "Recent domain registration" warning in the Extended Due Diligence section.
The warning indicates that the domain name attached to the listing was registered within the last 60 days.
ICANN regulations prohibit the transfer of domain names between registrars for 60 days after they're first registered, or transferred between registrars. Flippa can detect newly registered domain names, but not domain names whose registrar has recently changed - you'll have to research that yourself.
If you buy a property that shows the "Recent domain registration" warning, you'll have to wait for the 60-day period to expire before you can transfer the domain name to a new registrar.
This won't be a problem if you already hold other domain names with the seller's domain registrar, since transfers of domain name ownership with the same registrar aren't restricted. You'll be able to transfer the domain name from the seller's account to your account with the same registrar.
If you don't yet hold any domain names with the seller's registrar, the easiest way to take ownership of the domain will be to set up an account for yourself with that registrar.
You can also negotiate with the seller to transfer the domain name at the end of the 60-day period. In this case, make sure you can trust the seller, as they'll control the domain for some time after you've bought it.