A track record.
So far, you've said they had a special purchase of 2000 cells. What happens when they run out?
Luyan has been delivering grade A cells since they opened. They have an ongoing contract with EVE, not a one time purchase.
There are a lot of vendors that deliver quality cells, until people begin ordering from them. With Luyan, you know you will get what you order.
So far, I've seen you receive quality cells from Basen, that doesn't mean they are the only company capable of delivering.
The original poster asked for feedback, I posted feedback about my two positive experiences.
Edit to add, the original poster asked about 230AH cells, I haven't heard that Basen got a deal on those. I know Luyan buys different sizes of cells directly from EVE, because I've ordered different sizes of cells from them.