Conclusion: Yes, it is legit!
I sold my PS4 Pro on Decluttr and got $170 for it as promised on their website. The process was quick, I just had to sign up on their website and register my product and they sent me a shipping label (free of charge). I took my PS4 Pro and the shipping label to a UPS Store and it was done.
It took a week for my PS4 Pro to arrive to their facility, but they funded my account within 2-3 business days. Wow, this sounds like an advertisement. Haha
I wish I was getting paid to write this though!
Have a wonderful weekend,