Platinum

Platinum is the supreme currency in the game. The most important thing you can BUY with platinum is “slots” if your looking to increase your MR, as that is the only way to raise your MR, so platinum is critical to your MR game progression.

Methods To Get Inventory To SELL

Here are the platinum farming method ideas:

Run fissure missions cracking relics for prime parts and SELL them.
Run tier 5 bounties in the open worlds to get Aya. Use that Aya to buy relics from Varzia in Maroo’s Bazaar. Sell the Relics.
Buy mods and weapons from Baro Ki’teer to create an inventory that you will sell 3+ months later.
Riven Mods. Pick Rivens up from Iron Wake, Teshin, SP Circuit, do the challenges, then sell them.
Do Nightmare Mod runs and sell the mods.
Do Conservation for the rare tags and buy the Beast Claws Mods from Master Teasonai, The Business, or Son to sell.
Do Drift Mod runs and sell the mods.
Do Silver Grove runs and sell the mods.
Do Orokin Vault runs and sell the mods.
Rank up your Syndicates and sell the mods, weapons, or relics.
Collect complete r5 Arcanes and sell them.

Where and How to SELL

Use Warframe Market to undersand the current market selling price of your item/mod.
You list everything your SELLING on Warframe Market or in trade chat.
While your in game a buyer will message you about your item you listed for sale.
You will set your status to public, go to your dojo or be in your dojo, and invite them.
When they arrive you will start a trade session with them using the Trade Tower.
You will click one of your open item squares and select the mod/item your SELLING.
They will offer platinum.
Check the item/mod you selected is the one they wanted.
Check that the platinum they are offering is the correct amount.
Then accept the trade. That ends the trade successfully.

Trade Etiquette

Be polite always! Ignore any comments about your trade good or bad! Always say thank you and do your best to +1 rep your buyers on Warframe Market. Be the best!
Do not negotiate, the negotiation is already done when you set your price.
Do not accpet under payments (mistakes happen) and mention the price again and wait for them to correct it.
Do not accept over payments (mistakes happen) and mention the price again and wait for them to correct it. Be nice to your fellow Tenno to help them not make a silly mistake.
Do not play queue games, it is first come, first served, ignore all other buyers until your current trade is complete, there will always be more buyers.

These methods are just you doing the work and someone else is going to pay you platinum for it, nothing special, these methods are a regular parts of the game.