Bava Basra 84a: The buyer always claims that the merchandise is bad, even if he knows that it is not, and likewise, the seller always claims that it is good.

Rashi: One who acquires Torah via difficult and afflictions of hunger, he says 'woe to me for this affliction.'

R. Yonah: Also after buying the item, the buyer degrades and belittles its value in front of the seller.

R. Yonah (3:7): Lowliness of the Nefesh is called Ra.

Malbim: Normally, one who comes to buy something says that it is bad. Initially, he says that also the price is bad (he does not want to spend so much); it is bad for its price.

Rashi: When he goes (becomes) full of Chachmah, he will boast about the pain that he bore.

R. Yonah: When the buyer goes away and is not in front of the seller, he boasts about his purchase. This is connected to the coming verse.

Malbim: After he bought the item, he is happy that he bought it for a high price. This is a Mashal for not loving sleep; Torah is acquired via minimizing sleep and pleasure. At the beginning, while acquiring Chachmah, he says Ra Ra, for he thinks that the price - bodily exertion and abandoning sleep and pleasure - is high. After acquiring Chachmah, he boasts, like the coming verse explains.