Cash is always welcome on any transaction but you will be asked to prove you have enough to purchase a particular property with what we call a "proof of funds" document.
Sale terms are posted to notify a prospective buyer of the terms available for a particular property. Cash always works, conventional financing usually works but sometimes FHA loans will not work if a home will not pass an FHA inspection/appraisal due to condition. Or if located within a condominium association, the complex must be FHA approved. Some properties are in total disrepair and will not qualify for any financing.
Sale terms also reflect the sellers willingness to entertain a variety of offers.