这个很难说，得看具体的情况，例如如果有budget的情况下，如果甲很贵，乙很便宜，那么他就愿意用甲来换乙使得自己的效用更高。

别的情况也存在，例如我的效用曲线特别贪婪，我跟你说我愿意用一瓶可乐来换3套房子，你觉得我更喜欢可乐么？

best，

既然喜欢x，为什么要拿x换有呢？

这是一种假设，如果换的话，会怎样，从而判断更喜欢哪者

True, you should define what is "like" first. e.g. he likes things that can bring a higher marginal utility. Theoretically, "like" can change depends on his budget, his current endowment or any other stuffs. e.g. you like water if you have tons of breads, while you will like breads more if you only have water. You will like water if you are thirsty but like bread if you are hungry. This like is defined by marginal utility.

I roughly know what you mean. You think if he is willing to exchange large amount of A with only a small amount of B. This means he likes B more because usually this exchange is made by small amount of A with large amount of B. But, I should say, as long as this guy is rational and he is willing to give B for A, he should know that this exchange can increase his happieness at least at that time point. So you can not say his likes B more otherwise the situation should be reversed.

do you mean as follows:
whether one likes a or b better is decided by the  utility he can get from one .considering some special time and situations ,even one has more  a than b ,it is still possible that he likes a .eg :one was in hospital ,at this time ,he has more medcines than nutrients ,but he still need medcines .
but if we don not consider the special situation ,at the usual situation ,whether could we know one likes which better only by the number ?
thanks a lot .