For Realtors: If I list in MLS on my own, do I have to pay the buyer's realtor a commission?

For starters, you cannot list in the MLS 'on your own'. A minimum is a listing through a 'flat fee MLS service', and they are licensed brokers offering a minimum service for that flat fee. You will be required to state a percentage of sale price you are willing to pay a buyer agent if they bring you a buyer. If you offer nothing, you will get ZERO showings. If you offer too little, you will get FEW showings. Agents will simply byp your listing for other more lucrative listings.