If you know that you can place the betta, then if you feel you are up to the challenge, go for it. But be absolutely sure you can place the fish with someone who can look out for it before getting it, otherwise your quarantine tank is going to become that betta's permanent home. Do you have a sufficient supply of meds for these fish? While clean water will do wonders, some fish will require more intervention, and you want to have meds on hand, because you won't always be able to run to the store, or the store just doesn't have them.
Also, be prepared for losing some of these fish. I've experimented with quite a few sick bettas now (I have a flea market near my home that sells bettas, the lady at the store gives me bettas for free - she always has a wonderful selection of bettas on the verge of death from various illnesses and infections). I've found you can't save them all. Losing some of them can be sad, especially when you thought you were doing so well with some of them and then they just lose all progress and fade away, or suddenly crash.