Is having a realtor a worthwhile idea?

[Mike Troyke]

I just got my first verbal offer on a property for 259k. He had a previous offer on the table for 267k but the buyer wanted to use a realtor and taking a 6% commision would bring the actual net price to 251k. He said he would take his off 3% for the previous offer and drop it  259k and not use a realtor. My question is now as the new buyer am I able to use a realtor without it affecting the price? My understanding is that when buying a property a realtor does not cost you anything. Also is the work a realtor does worth hiring or is it things you can figure out as long as you do your homework.