I check river, willing to call up to x

[partygirluk]

I see this often in this forum, typically when holding a good not great hand on the river. I would like some clarification. From this I infer that the bigger the bet, the less likelihood of a bluff.

E.g. Pot is $1000. You check, willing to call up to $500.

Since you are willing to call $500, you are assuming that he will be bluffing 1/4 of the time (or more) for your call to be profitable.

If he best $1000, you fold, which implies that you think he is bluffing less than 1/3 of the time.

But for a typical opponents, wouldn't it be typical for him to bet larger when bluffing? Couldn't it be that when he bets $1000 he is bluffing 1/2 the time, when he bets $500 he is bluffing 1/10 times, so infact you should check intending to fold for $500 but call for $1000?