All I have to say is welcome to capitalism. The principle some of you are missing is the law of economics that says an item isn't worth a cent until it is sold. In other words market value is determined by what the market is willing to pay for a given item.
At the start of a season prices are at their peak, as the season goes on the left over stock costs money to house and store and in the case of livestock it costs money to feed them. It may be worth while to sell the animal for less to cut your losses. The trick is to sell them just cheap enough to get rid of them all quickly, before they start costing you money while you hold out for that higher price.
As an example we'll use a clutch of hatchling corn snakes. Now let's say you sell them for $40 each and you sell all but 2 of them right away, after say 4 meals or so. The remaining two you are then stuck with. It costs about $52 per year to feed a corn snake so the question is how long are you gonna wait before you just give these snakes away because they are actually costing money? After 40 weeks they've already cost you every dollar you were hoping to get for them so it makes sense that as time goes on during the season the prices on the left over stock will fall. The prices must fall because the vendors or breeders want to cut their losses and get that stock out the door, they would be stupid to hold out for the higher price. The last thing they want to do is sit on it, pay to feed it and have no room for new stock the next season.
The lesson is to be competitive at the start of the season, move all your stock and not rack up costs from keeping your prices high and being left with the stock.
I feel a little light headed... maybe you should drive...