When you are talking about the most collected player and a graded card, it is different, but as a general rule, an offer of $150 cash on a card with $300BV is normal!
But I don't think it is necessary to make a negative thread about it! People will always look for a bargain! If you want to sell on places like this, you gotta get used to it!
Also, when you advertise a card with a 'value' of $10,000, and openly say that you will accept $4600 Buy It Now, why WOULDN'T people think that you would accept less than half BV on other cards???