If you found it in the MLS, the seller has listed with a realtor and you will have to go through the sellers agent. They have signed a contract with them, so you cannot contact the seller directly ethically. If you choose to contact the seller directly, you would still have to buy the property subject to the sellers commission unless you work something out with the seller to wait until the listing is expired. I have had calls from people before who are listed and wait until the listing expires before I buy the home, but I do not actively pursue them. If I find a good deal in the MLS, I make an offer through the sellers agent directly or I use my own realtors to do the offer.
Waiting to the listing expires doesn’t help either because most listing contracts state that any offer that comes in x days/months after listing expires is still subject to a commission. Also, ANY offer that comes in because of the agent’s advertising is subject to commission. If you found the deal because of the agent’s effort, then a) the seller has a contractual obligation to pay the agent, and b) you, as an investor, should have an ethical obligation to pay the agent.