Shabbos 64b - Ma'aris Ayin

Rav says that anytime chazal forbid something on the basis of ma'aris ha'ayin, it is forbidden to do even in private when no one else is watching. The gemara cites two Braisas whether an animal can be in a chatzer (not reshus harabim) while wearing a bell on shabbos which looks like it is being taken to the marketplace to be sold. The gemara says that the two braisas are dependent on a machlokes tana'im whether we forbid ma'aris ha'ayin even in private, as Rav holds, or only in the public eye. There is a machlokes whether one can hang out clothing to dry which gives the appearance of it being laundered on Shabbos. The opinion who says it is permitted to hand it out in an area where people cannot see it is against Rav, and the other opinion conforms with Rav.

Tosafos says that some prove that we don't pasken like Rav based on a gemara in Chulin which forbids Shechita in a hole because it looks like it is being done for avoda zara, but permits it in a chatzer. This seems to imply that so long as it is being done privately it is permitted. Tosafos rejects the proof and says that the advantage of the chatzer is not that it has less exposure to the public eye, rather, in a chatzer people assume you are shechting in a hole to avoid dirtying the chatzer. In other words, when the advantage of the private area is merely less exposure, chazal still maintain the issur. But if the advantage of the private area is that the circumstance avoids the entire issue of ma'aris ayin, it is permitted. Based on this, it seems to me that one may hang coats and jackets that are wet from the rain in their bathroom, without any concern. Although the fact that it is being hung indoors doesn't avoid the ma'aris ayin concern, the way in which it is being hung and the place in which it is being hung doesn't mislead people into thinking that it was actually laundered on Shabbos. The Sha'ar Hatziyun 301:212 says something similar, that if the garments aren't spread out as they are typically done after laundering, there is no issur.

There is a Tosafos in Kesubos 60a who says that although we pasken like Rav and forbid ma'aris ayin even in private, that is only when the being watching would suspect you of an issur d'oraysa, but if they would just suspect you of an issur d'rabonon, it is permitted in private. The Magen Avrohom asks from the gemara in our sugya that says that according to Rav (and the tana'im that forbid spreading out clothes even in private) it is forbidden for an animal to go into the chatzer with a bell because people will think that it is being taken to the marketplace. Selling an animal on Shabbos is only an issur d'rabonon, yet the sugya assumes that it would be forbidden even in private. This seems to be clearly against Tosafos? The Maharsham says that based on Tosafos 150a that the business shevusim that are learned from the pesukim in Yeshaya are like d'oraysa, it could be that selling an animal in the marketplace can be considered an issur d'oraysa.

The Biur Halacha 301:45 writes that since there are some poskim who reject Rav and hold that ma'aris ayin is permitted in private, one can at least rely on Tosafos who says that it only extends to private areas when the person would suspect you of violating a d'oraysa, not if they would only suspect a Rabbinic violation. Although he points out that our sugya doesn't seem to support the distinction of Tosafos, he doesn't offer any explanation to reconcile Tosafos in kesubos with our sugya.
See also the last pischei teshuva in hilchos chala (yoreh deiah) where he discusses whether Tosafos in kesubos can be relied on l'halacha.