They seem to have a clean slate - I was unable to find any customer reviews or complaints.
One way to check on a supplier's customer service is through the response rate of the email you send them although this may be a bit subjective. If you can I suggest giving them a call and see how they respond to your call - to your questions and inquiries.
When (and hopefully) you are satisfied with the service you may try a sample order to be able to check their product's quality.
Hope this helps.
If you do proceed to buy from this supplier, do add a review to the supplier's profile page! :)