这个我懂得，大家都懂得。 但是，我不知道楼主懂不懂得最基本的定价。虽然，我知道你的附件会有人下载，总觉得你设定的价格水平很随意。如果出于热心的分享，我感觉你也不会设定高价。可能你在国外购买了一本电子版本，我知道也很贵，但是既然你都分享了，定高价就有些不必要了。。。个人观点，

You are absolutely sensible.
I talked to the owner of a supermarket to reduce the prices of her goods as she had been serving the local community for quite while already. She said she needs money to pay for the bills from the suppliers who had never reduced the prices.
Sad!!