The usual precautions is to make sure the person who is selling the item, actually owns the item.
Ask for a contact number, and move the conversation to Whatsapp or Telegram. OLX silently censors any message with the words 'Whatsapp' or 'Telegram', the message never reaches them but it shows as sent/delivered to you. So ask for a contact number, and add that number to your contacts and continue the conversation on Whatsapp/Telegram.
And once there, ask for a video call or extra photos. Exchange photo ID's to verify your identity and theirs. If you're transferring money before receiving the item, make sure the bank account details match the whatever is on the Photo ID they shared. If you can, arrange for a courier yourself through a dellhivery or a free shiprocket account instead of relying on them to ship it at their convenience.
And lastly, even with all these precautions, don't pay any amount that you're not okay with losing, if the seller turns out to be a fraudulent person. I haven't actually been scammed by anyone OLX in these many years, most people there are just regular people looking to offload things, but plenty of others have been scammed with high value items. Generally, if the price is too low for what you're expecting something to be sold at, it's a scam.