I have personally never been to decathlon, but like metro cash and carry, decathlon has been given permission to operate in india to sell to wholesalers only, wchich is why only companies and shops can get the merchant card that these stores offer. Now u can say, this is a farce, but you will have to tell that to the govt which feels that citizens tax paying, salary earning, middle class citizens should pay a higher price while it pretends that it is protecting the kirana stores ...
Am not sure about the discounts at all ...
Decathlon is a model similar to that of Metro Cash and Carry. It is a B2B or a Business to Business model sale only. Therefore you need to have a sales / service tax registration to get membership.
Since they promise whole sale prices normally significantly lower than their retail prices (generally to allow business who buy from them to earn a decent margin on the MRP) the government prevents retail sale (apparemtly protecting smaller businesses) and only allows a B2B model.
However any person who is a business owner can buy and so a lot of us have memberships though we are not into this business.
In most other countries, decathlon membership only gives you loyalty points. Anyone can walk in and buy from their stores.
Hope this answers a few questions.