I have those problems once in a while. I called to price a compressor once. They told me the price and had plenty in stock. Showed up a week later to pick it up and was informed the compressor was no longer available, and had to go through all kinds of hurdles to get what I needed.
They get me when I call to get a price on something... "it's about $300" they say. First time I heard that, I figured it was somewhere between $295 and $305. Not so... turns out it would be closer to $350 or so. Now I make them give me the exact price down to the penny with a quote number. Minor price differences like that may not be a big deal to the big boys, but to small trunk slammers like myself, it can take a bite out of the bottom line when bidding something out. Even if I have to go back and redo the estimate, it still takes time out of the day, I have to get it re-approved, go back and forth and so on... time is money!