As someone who is absolutely obsessed with all things Madewell, I don't understand what's with all of the negativity surrounding their customer service. As a disclaimer, I'm not related to the franchise in any way, shape or form nor am I associated with J. Crew and any sister brands.
I can't speak much about the in-store customer service (as issues that arise may be a regional problem) except that I have never had a bad experience in-store. As far as my online experience goes, making purchases online is super easy. Their formatting is coherent, and for the most part their online images are an accurate representation of the quality/style of the clothing in person. Madewell is true to their name as their fabrics are sturdy, opaque, and stand the test of time well. The only exception to this I'd say are some of their basic tees, which may shrink with wash. As far as their jeans and shirts are concerned though, they're all amazing styles with great quality material.
Now onto online customer service. I have called Madewell customer service for general problems probably 4 times in the past three months, and they have all been exceptionally helpful and friendly with all of my concerns. I'm going to share my most recent one that particularly stood out as a testament to their dedication to customer service. I recently graduated college and have already left the state to visit my relatives for the summer. I recently made a purchase for two tops online (no brick and mortar store near me...), but I accidentally sent them to my university PO, which I no longer occupy and have no way of retrieving items from. Even though I was definitely at fault for not being more careful about my shipping information, the customer service rep. Was more than happy to check for rerouting. When she found out it was no longer an option, she stayed with me while I contacted my university to see if it could possibly be forwarded from there. When I found out it couldn't, the rep. Kindly offered me a full refund and stayed with me, helping me find alternatives to the items of clothing in that order (as the originals were sold out in my side). She was so kind and not at all annoyed with me, despite the situation being my fault. At the end of the day, Madewell really stands by their customers and our loyalty is sincerely acknowledged and reciprocated from their side.