A seller under real time pressure, facing a firming possession date on their own next home or a health or estate deadline, will often accept meaningfully less for a cash buyer's speed and certainty than a seller with no timeline pressure at all.
Condition also changes the math. A cash buyer waiving a financing condition still often keeps a home inspection condition, so a seller expecting no discount at all should expect at least a repair conversation once that inspection, typically $400 to $600, turns something up.
The right way to answer this for your own house is to compare actual competing offers side by side rather than assume a percentage in advance. Get your hand-reviewed valuation from Joel Dyck.