Have ordered quite a few items in the past year and I'm a satisfied customer.
Prices are usually good, quality is the same as other places and shipping is free. Delivery lead time is variable but can be very fast (5/6 days to France) or very slow (5 weeks) however Banggood isn't a postal service company so I can't blame them when delivery is slow.
I have had to use their customer service once for a parcel that had never arrived and I was offered the choice of a refund or resend.
I never had to return goods to Banggood so I cannot tell how that's handled.