If drop shippers provide bad service they get "dropped" so for the most part they are pretty good. The bigger challenge is communication and returns. Hopefully you have a shopping cart that automatically sends out a note to the drop shipper and they automatically send you a note so you can respond to customer requests. You have to be careful about the return policy for example it would be very confusing for a customer to have different return policies for multiple items so you may want to keep it consistent but make sure that your suppliers have the same guidelines as you or you could end up paying for a lot of returned merchandise.