Some agents will and some will not show your home. Why? I have heard agents complain that working with FSBO's means twice the work for half the pay. Without agent representation, the seller will be heavily relying on the buyers' agent all through the transaction. That is what I have heard and it is not the way I do business. Maybe some of the agents who won't show it can add to that reasoning.
I will show houses that are FSBO and here's why I do it: I believe it is my responsibility to know my market area. All of it. Not just listed properties, but FSBO's as well. This way I can represent my buyer's best interests. Before I show a property, I will drive through the neighborhood and call any of the FSBO's that I see for sale to see what they are offering--just in case it is what my clients are looking for, Then, if we run across one while we are out shopping (one that I didn't know about) I will pick up the phone and make the call with my clients in the car to see if that property is right for my clients. And, if the seller will not cooperate with the FSBO, I will still recomment they see it on their own and will do what I can to help them through the transaction should they decide that is the house for them.
Having done that in the past (helping a client work with a FSBO who is not paying a buyer agent commission) I can tell you that once it worked out for my buyer and once it did not. The time it did, the deal died twice because the seller didn't know how to negotiate and work the transaction through. I did a lot of work for my buyers, advising them every step of the way, and they got the house they wanted at the price they wanted. Those buyers have been an unbelievable source of referrals for me! The second time that it did not work out, those clients bought a house working with me, knowing for sure I always had their needs first and foremost.
I would just add that I believe that it doesn't matter so much what company lists your house as much as it matters what agent lists your house. There are good agents and bad agents in all companies. Find an agent with a good marketing plan, a proven record, and price your home right. Price is key. If you are priced right and have excellent advertising exposure, your house will sell.