膏药 (gāoyao): medicated plaster

膏药 is a staple of traditional Chinese medicine - black herbal paste on fabric, applied to aches in the back, shoulders or knees. Street stalls selling 狗皮膏药 ('dog-skin plasters') at temple fairs gave rise to the idiom 狗皮膏药 meaning 'cheap quack remedy' or, by extension, anyone hawking dubious stuff.

mistakes

The measure word is 贴 ('patch/paste'), matching the verb 贴膏药 (to stick on a plaster). Don't use 个.