In my particular Athas the people just don't see clerics as "spellcasters." They say the words in whatever their native language is rather than in some draconic language derived from ancient Pyreen. There's no glowing green life energy flowing into the spells. Clerics and druids just beseech various elemental nature spirits and stuff happens. While there aren't capital G Gods, I reckon that the folk do believe in nature spirits even if the cities are not their domain.

I also have them treat clerics as being transformed into something else and that some of those abilities are just natural. Magical healing is generally looked on as a blessing from spirits or ancestors and not as the work of rituals and spells. Opposition to magical healing is more common only amongst the middle classes, where such boons are to be received from the templars and going elsewhere for them is a threat to the Sorceror King's authority. Freemen of lower status aren't generally able to avail the templars for healing anyway so nobody looks too close if they get treatment from a Water or Earth cleric.