When a user sends his Btc to sell to the platform, he receives it, once he receives it the post activates and you can now share it to buy, you wait for the buying user to send you the screenshot of the receipt (you will also notice that you received a bank transfer out of nowhere) and you will receive an email notifying that someone took your offer for you to release the bitcoins, once released they pass into the power of the buyer, and the buyer has to remove their bitcoins to a Wallet that belongs to them
I want this to be used by the entire community (I currently have the site with the Mexican currency but if you want operations to be done in USD I can change it, just contact me through the website and tell me) to make the ecosystem a better place
You are the middleman between buyer and seller, is it? So you ensure the transactions go smoothly and legit, otherwise, there aren't any guarantees for the parties involved, since a BTC buyer can deposit fiat on the BTC seller's account, but the BTC seller might not send any Bitcoins in the end.
And if you are working as middleman, aren't you charging any price for your services? How will you keep your platforms active and operating? I suppose there are costs involved, besides the time you spend there.
Exchanges charge indeed very expensive fees over transactions, but that is the cost of running the business... It would be great if every Bitcoin enthusiasts had the possibility of only transacting through P2P, so we could have access to fair prices when buying and selling, but that is unfeasible for most of us, because there aren't people locally to trade within.
Your service, for an example, wouldn't be accessible to me, because I'm not in Mexico, and to do foreigner banking transactions is just too expensive. That is actually one of the reasons why El Salvador introduced Bitcoin as legal tender on their territory, so native citizens living abroad could send money to the country through BTC, instead of fiat paying exorbitant fees to the banking system.