Hi Lynn,
from my experience, i think the most important things are: 1. they have the products of your niche at competitive prices, or they can offer a wide range of other products which could be profitalbe to resell, ofcos you have to do some research and compare average ebay retail price and the wholesale or dropship price they offer. 2. no dropshipping fees and minimum order. 3. service is fast and secure. 4. real time stock availability on the online storefront so you won't have to wait for new stock to arrive after you have collected payment from your buyer and promised the shipping time. 5. good customer service, the maximum average respond time should not be over 48 hrs 'cause sometimes you ask them questions on the behalf of your buyer, you have to get back to your buyer asap b4 the listing ends, so you won't lose any potential buyer because of delay in answering questions. there are also some more obvious points such as the profit margin you can get and their experience in dropshipping business... that involves a lot of work and i suggest to test out their service and the quality of products first by ordering yourself a little gift
, or, run a search on google to see if they have been involved in any scam and see what others are saying about them ... these are the first things i consider when choosing a dropshipper to work with, hope that helps