Unfortunately, the lead test swabs are not terribly accurate, giving both false positives and false negatives. At best, they give an indication that you need to inquire of your supplier or send the goods out for more accurate testing. If you are selling in California, you do need to work at meeting CA rules.CA has some very specific rules about what kinds of lead tests are required and what labs are approved to do the tests. See California's "Lead in Jewelry" Web pages for lab information..
The Rings & Things web site has a summary page covering the rules for Adult jewelry. (Children's jewelry has much stricter rules.) See the Rings & Things Jewelry Safety page for details.
As far as I know, Rings & Things is the only distributor or on line seller listing the CA lead class for nearly every item in their on line store. (Click on the details button on any item to see the CA lead class.)
Despite the negative publicity given to children's jewelry and toys made in China, I've found Chinese findings manufactures to be more knowledgeable about lead issues than most US firms. We have to ask the right questions. We have to confirm the products with expensive testing. But we are able to supply lead free or low lead products that meet CA rules for adult jewelry.
You need to ask your suppliers for that same level of assurance about the products you buy from them.