I agree completely.
There is actually a spelling rule that disproves "afedersin". The rule says that, words are spelt together if there has been a sound change in one of the words:
For example "red + etmek" is pronounced "reddetmek" with two D's, hence spelt together.
Other such examples: his + etmek - hissetmek; hâl + etmek - hâlletmek
But for example "terk etmek" is spelt as two words, because there is no sound change. The same thing goes for "fark etmek".
Now, if it were "afetmek", you wouldn't spell it as one word, as there would be no sound change. And it would have been "af etmek".
Plus, everyone clearly pronounces it with two F's. So I don't know where this "afetmek" thing even comes from. Do they say "beni afet, aşkım" for instance? ...
the truth is that these words which are originally arabic have a "tashdid" at the end which means "emphasis" . but in Modern Turkish few of them are being used separately like "hiss" or "redd" and most of them have turned into verbs. so when you say "hissetmek" or "reddetmek" actually you do what you have to do. and these are absolutely different with "terk etmek" or "mahv etmek" which are not -tashdid words. anyway, despite spelling them as one word or two which to me is a grammatical deal, the double endings in aff, hall, redd, etc is something related to the words' origin and is mandatory.
I would like to add a little piece of info that will support what is being said here. The "shadda" ( ّ )in Arabic actually indicates that the letter should be written twice in that position, the first in consonant sound and the following-same letter- with a moving or vowel sound (shaddah replaces the repetition)! To clear the confusion, in Arabic there are no vowel letters, the sound of a letter is indicated by a mark above or below it. For example: nْ = n, nَ = na, nُ = nu, and nُّ ( that is a ُ on top of a ّ )= nnu...etc!
Banyo refers to bathroom/washroom usually with a full bathtub and/or shower (duş), but it can also mean bath. A Turkish bath, however, is called a hamam.
Tuvalet refers more to a washroom or restroom with a toilet and can also specifically refer to a toilet.
"Where is the washroom"?(literally "toilet") = ("Tuvalet nerede"?).
"I'm going to have a bath".= ("Banyo yapacağım").
"Hamamlara gittiniz mi"? = "Have you you been to the "Turkish Baths"?
I hope this helps to clarify the difference. :)