My updated recommendation list after few years. Ordered by Alpha.
(P) = Platform; multiple sellers list through this site, so always check the seller, not the site.
annsfabulousfinds.com - one of my favorites. Sells lots of Chanel, Hermes. Also on Portero, Ebay.
bellabag.com - based in Atlanta, GA, good selection of Chanel. Also on Ebay. Also on SnobSwap, Ebay.
boutiquepatina.com - Based in California. another one of my favorites. Specializes only in Chanel and Hermes. Good vintage selection. Also on Ebay, Portero, SnobSwap.
elady.com - Specializes in various brands. Based in Japan. Good vintage selection. Also on Ebay, but direct from their website is 10% off, and new users can get an additional 5% off.
fashionphile.com - Based in California. Started out as an LV specialist but now is one of the largest resellers in the U.S. for pre-owned bags. Good selection of Chanel and Hermes. Also on Ebay.
fmasarovic.com - Specializes mainly in Chanel. Based out of Japan, but super communication and service as owner is North American. Sells through Malleries. Good vintage selection.
luxetouchbags.com (formerly Chanel Touch) - Based in Canada. Specializes only in Chanel. Great vintage selection. Sells through Malleries and Portero.
luxurygaragesale.com - large selection of pre-owned Chanel with huge network. Also has a ton of RTW which is awesome. Also sells on SnobSwap.
madisonavenuecouture.com - Based in NY. Specializes in Chanel and Hermes. Mostly brand new selection, over retail. Also on Portero, Ebay, Tradesy. Ebay and Tradesy name is La Clochette
malleries.com (P) - Website based in PA, but sellers mostly from Asia. Great online shopping mall of various resellers. Site does not disclose origin of bags so you should check for customs considerations prior to purchase, as all sellers vary.
onlyauthentics.com - Based in NJ. Specializes mainly in Hermes and Chanel. Unique, collectors' pieces for the Chanel or Hermes collector. Also on Malleries, SnobSwap
opulenthabits.com - Former department store SA turned shop owner, great network and access to good Chanels and Hermes. Also sells on Tradesy.
portero.com (P) - Based in NY, but sellers from everywhere. Portal site that does not disclose seller identity. Ann's Fab Finds, Boutique Patina, Trendlee and many other sellers sell through this portal. Many Asia sellers (check or inquire for import duties). Often, buying directly from their own site is cheaper if you can find out who the real seller is. (Try a Google Search of a few sentences from the item listing description, can help)
sacamore.com - Based in NY/CT. Great selection of some Chanel but more Hermes. Main site is through Malleries.
snobswap.com (P) - Newish platform that is set up like Malleries but features more brick-and-mortar stores, almost all from the United States. Good selection of Chanel, but a bit harder to navigate.
strictlypursonal.com - Good selection of Chanel. Reliable seller. Sells on Malleries too.
therealreal.com - Based in California but ships from New Jersey/NY. Large consignment site that is not a portal. Photos are on the scant side, but great selection and great prices.
trendlee.com - Based in New Jersey. Recent heavy hitter of Chanel and other bags. Great pricing. Also on Portero.
yoogiscloset.com - Based in Washington state. Great consignment store with good selection of Chanel.
Ebay sellers (other than the trusted sellers above who list on Ebay):
fashionhulu - another one of my absolute favorite Chanel sellers. Takes many photos and very honest listings. I love her.
bagswithstyle90210