Normally you would hook it up to your bank and deposit USD into your account. If this isn’t an option, then next thing I would look at is if there is an exchange in your country that can be hooked up to a bank account. If that isn’t an option, many countries have BTC ATM/cash machines. This would require you to convert to BTC first I think, idk if they accept ETH. It seems normal that you would need a little ETH to convert transaction costs. What country are you in ?

Create an exchange account, like Coinbase or Gemini. Go to “receive crypto” – select ETH (not ETH classic), you will get an ETH address (42-character hexadecimal address derived from the last 20 bytes of the public key controlling the account with 0x appended in front.). Send this to your buyer and now they can deposit funds in your account. If they are legit, this will be acceptable to them, otherwise they are running some scam.