Hi Zoe -
You might also consider KEH
https://www.keh.com or MPB
https://www.mpb.com/en-us/. Both companies focus on used camera equipment so there tends to be a lot more to choose from than the other companies you mentioned.
I had one excellent experience with MPB when I bought a used "like new" macro lens. It was definitely as described. A second purchase wasn't so good because they sent the wrong lens but quickly corrected the mistake.
I've bought a few inexpensive camera items from B&H and had a good experience. I had to return something and their customer service was great. I was considering buying a used lens from B&H they rated a "10" or like new but decided to buy it brand new from another camera store that offered a great package deal on Amazon.
You need to compare the warranties offered by each company and the return policy in case you don't like your purchase.
Hope that helps!
Ann
