As a real estate professional, my take on an for sale by owner (FSBO) is an owner who doesn't want to pay a realtor commission to sell their house. From the buyer's point of view, here are the pitfalls in dealing with the owner of a property, rather than a real estate professional.
1. Most buyers are very uncomfortable having the owner tour them through the home. They will probably regale you with how they did this to the home or this is where there kids did that. First of all, you don't care. Second, you may not ask the hard questions or feel free to speak freely about the property with the owner right there. Most of my buyers feel uncomfortable even if the owner is present during the showing.
2. Most likely, the owner is not a real estate professional. So, they don't really know what they are doing. If you are trying to buy directly from them or even if you are using a Realtor, it will be difficult. Because they are not in the industry, most owners think their home is worth more than it is and do not know what to reasonably ask or take for the house.
Also, as a buyer, the law affords you some protection regarding disclosures for lead paint, radon, and problems with the home, plus equal housing (non discrimination). A single home owner selling their home will likely not comply with these or even use the correct contracts, etc. And in some cases, the law doesn't require them to comply. This could result in problems later with closings, mortgage approval, or problems later with the home,etc.
So - it is a deal to use FSBO instead of dealing with a Realtor. First, you won't save any money and it may cost you money. Ultimately, the answer is as simple as this. Would you go to court without a lawyer or perform your own surgery? No, the professionals have your best interest at heart and will ensure you do not get a lemon.