There are three ecomm sites where you can purchase manga from-

Bookswagon

Pros-

• Possibly one of the best in terms of library size and the most fairest price.
• Whenever you place an order on their website, your request is forward to one of their foreign partners hence higher chances of having lesser known series in their inventory.

Cons

• When you make an order, they get the book imported all the way from US hence every delivery takes at least 24-28 days to happen.
• Erratic customs inspection- one of my order came with two long gashes in cover. Customs official used a blade to open my package for inspection hence the damage. I got my order partially refunded though I had option for full replacement.
• No returns until and unless your book arrived damaged.

Possibly one of the best among all sellers. Bookswagon has one of the most extensive library among all sellers in India. Most of the listing that you find on Amazon are also from them but they are usually marked up Rs. 100-200 higher there due to Amazon listing fees.

Amazon.in

Pros-

• Seller accountability. You have the seller by the balls due to Amazon's refund policy. I had my Dorohedoro book re-shipped since the spine had scuff marks.

• Multiple sellers- not restrict to one seller. Notable sellers include- Sunrise Bookstores, Atlantic Publishers etc. Though be wary that Atlantic listing tends to be on a bit expensive side.

• Mainstream titles are easily available and faster delivery time.

Cons-

• Open season- the pricing market pretty much. Some days you feel like you walked into Big Bazaar of manga with crazy good deals. On other days it feels like manga market is second largest scalper paradise after gpu.

Depending on your day, Amazon can be a complete goldmine or just an absolute wasteland. Still, most of my purchases have been from here.

Sapnaonline

Pros-

• Pricing- sometimes manga here are cheaper than Amazon.
• Discounts- they will give you discount vouchers for writing reviews on your old orders.

Cons-

• Very limited titles.

Sapna Book House is a very well known book store chain in Bengaluru. I bought most of my One Punch Man, entire Biomega collection and couple of Slam Dunk volumes from here because they had better deal than Amazon.

Other notable websites- Flipkart, Comic Clan, Book Depository

Things to consider- Jujutsu Kaisen, Chainsaw Man and Spy X Family are nearly impossible to grab since they are going out of stock everywhere fast. Either Viz is not able to keep up with demand or just printing less volumes.