Speaking from recent personal experiences.
It depends on where you will be getting from.
The refurb market is one that is varying in terms of both item and condition description with little to no common standard to base them on except for pictures posted and seller's descrptions.
I.e. an item rated very good and mint or 9/10 may not necessarily be as such. Pictures can be deceptive (to a certain extent) and if one is a perfectionist expecting a mint laptop - be prepared to get disappointed. Realistically there are dings and scratches - some more than others. Most sellers are understanding enough to know this and most have a motto to let users check first / reject the laptop.
These laptops (mostly business series models like elitebook and thinkpads) are often decommissioned laptops that are sold to exporters / firms who then refurb them / test them - insert a new hdd, clean them up and then sell them off. Condition can be a big (?) since they are of age - some laptops can approx 3 to 4 years - therefore it is advisible to check on terms of warranty (in house / manufacturers)
Some firms give new batteries (mostly 3rd party batteries) and some dont - only describing battery life in their descriptions - would advise you to check on that as well.
Purchasing a 3rd party battery isnt expensive - some less than $50 - however that adds to overall costs.
What are the things to take note of if considering buying a refurbished laptop?
The processor may be 2 or 3 generations older, and the casing may have a few scratches or markings.
Do sellers of refurbished laptops replace the old battery with new one from OEM or third party? Or it will last only 30 minutes fully charged then black out?