Shulchan Aruch, Orach Chayim 153:21:
אין לקנות מעילים שנשתמש בהם הדיוט לתשמיש קדושה
One must not purchase for holy use garments that a commoner used.
"Holy use" here includes use as the cloth cover of a sefer Tora (Rama OC 147:1). One cannot, therefore, buy someone's poncho for covering a sefer Tora.
Does this halacha (as is sort-of implied by its wording) apply only to an object that will be used long-term, or regularly, for a holy use? Or does it apply even to an object that will be used, say, once for a holy use: one should not take someone's poncho and use it even once to cover a sefer Tora? A sourced answer would be ideal.
Now, a cloth the sefer Tora rests on also is considered to have a holy use (Bavli, M'gila 26, "כיון דחזינא דעייפי ליה ומנחי סיפרא עלויה אמינא תשמיש קדושה הוא"). So, if the answer to my first question is "it applies even to something used once", then how do we take someone's talis and lay it out for a sefer Tora to be read on (as is frequently done on Simchas Tora and in a mourning house)?