Investors- Real Estate Agent to make offers???

Hi, Trying to get an idea whether you typically work with a real estate agent on a property you've located yourself and intend to make an offer and negotiate . Either for wholesale or flip. I analyze risk and negotiate settlements in my regular job and I'm very comfortable in this arena and professional in my formal offers, but have run across sellers' agents lately who keep pressing me re whether I'm working with an agent . Would appreciate your input.