Shavuos 45a - What is a Shavuas He'ses?

Rashi in the mishna writes that when the ba'al habayis makes a claim against the storekeeper that he has payed and not received the produce, the ba'al habayis swears a "shavuas heses" to collect. Rashi does the same thing on 46a by referring to the shavua in the mishna as a shavuas heses d'rabonon". Tosafos 46a and Tosafos 48a(but is on the mishna) asks that in the time of the mishna, the concept of "shavuas heses" didn't exist and was only introduced by Rav Nachman as the gemara brings on 40b. Tosafos proves this from the gemara in kiddushin 43b which uses a language of - והשתא דתקון רבנן שבועת היסת, implying that until the period of the amoraim, the concept of shavuas heses didn't exist. Actually, Rashi himself 48b says exactly like tosafos - וכשנשנית זו בימי התנאים עדיין לא תיקנו שבועת היסת כי בימי רב נחמן תקנוה. Being that rashi seems to admit that shavuas heses was first introduced by Rav Nachman for one who is kofer ha'kol, how can rashi refer to the נשבעין ונוטלין shavuos that are discussed in the mishna as a shavuas heses? The Ran at the beginning of the perek explains the opinion of Rashi that every shavua which is not d'oraysa and only d'rabonon can be called a shavuas heses. The term "heses" as defined by rashi 40b, doesn't refer specifically to Rav Nachmans institution of swearing on denying the entire amount, rather it is a language of "suma" - placing or persuading. Any shavua that is placed on the person m'drabonon is called a shavuas heses. Rashi 41a clearly indicates (as the Ran explains) that all shavuos d'rabonon are called shavuas heses, because the gemara is speaking about shavuos d'rabonon in general and rashi uses the term "shavuas heses". Therefore, the shavuos listed in the mishna of נשבעין ונוטלין were instituted by the tana'im and the shavua of kofer ha'kol was instituted by the amor'aim (rav nachman), but both can be called "shavuas heses". The Ran seems to understand that the commonality of all shavuos d'rabonon is that the chachamim so to speak convince you to swear even though the din doesn't require it, and therefore they don't involve nekitas cheifetz - holding a davar shebkdusha such as a sefer torah (as rashi writes in kesubos 88a - although tosafos 41a disagrees from the fact that the gemara doesn't mention this to be the distinction between a shavua d'oraysa and a shavua d'rabonon). Both Tosafos 41a and the Ran disagree with Rashi and hold that even a shavua d'rabonon requires a nekitas cheifetz. The Ran holds that the נשבעין ונוטלין of the mishna require nekitas cheifetz but not the shavuas heses of rab nachman, whereas Tosafos seems to hold that no shavua d'rabonon requires a nekitas cheifetz.