I think this can go either way based on so many variables. However, if you choose to go with a realtor, make sure you do research and interview to find a good one! A good realtor can be a great asset and definitely be worth the cost in commissions, but bad ones can potentially crush profits. Just like any profession, some are lazy, inexperienced, unethical, etc. so do full interviews! If you find a good one, keep them on your team! Here's a real life example that I experienced...
I met with a realtor who wanted to list my property at 273k. I knew this was low and that all she did was look at a few comps and match price per sq ft. Luckily, I knew the area very well to know this was low. I ended up listing the home and getting it under contract in 2 weeks for 290k just paying 3% buyers agent commission. So, let's do the math...I gained 3% (a little over 8k) plus 17k in profit for a total of over 25k in extra profits! Now, this was a hot area and I knew it would sell. Not every case is like this.