When you list your property with a listing agent, that listing agent can assist you at the beginning of the listing discussions with giving you a net to seller sheet, that states some app. numbers of items you need to pay for as the seller, and yes you are right one is the full commission percentage on the sale price, which of course you do not know until you have a fully negotiated and signed contract.
But then there are closing costs, recording fees, attorney fees, title & title company fees, possibly a transfer tax although Utah may not have one, surveyor fees, all outstanding taxes etc. Once you talk with an experienced Realtor in Salt Lake City, he or she will be able to give you at least a good estimate of what your costs will include and how much it will be.... So ask your listing agent to give you that information based
on experience from other closings....
If you need a referral I gladly would give you the names and contact info of trusted Realtor Colleagues of mine, just let me know...