Do you believe companies when they say?

You can always confirm with the charity.
On a site I belong to, a woman organized a fund for March of Dimes, and said she made a donation..but produced no receipt. People contacted March of Dimes, and they had no record of it, and were extremely upset. I don’t know what ever happened to that money. That’s not a company though.
When our cat recently was put down :( the vet said they donated a monetary donation to UofPenn Veterinary School in her honor. I choose to believe it.

I do if they are a respectable company and a respectable charity. For example, I believe Black Phoenix Alchemy Lab when they say the proceeds of my perfume, 413 US 15 Miller vs. California, are going to the Comic Book Legal Defense Fund. It is because I know the fund, I know the company, they both list the item, and they are both trustworthy.

Yes, I believe them! There’s a great article on the how’s and why’s, here.

I own a small business. We often run promotions for charity. We hang the letters of gratitude on our walls, so our customers can see how they’ve contributed.

I don’t believe any word any company says without looking into the facts myself.

If the company is publicly traded, they file shareholders reports which should contain figures of how much they donate to charity. If the company is private however, there really is no way of verifying beyond taking them at what they say, which I don’t.

i believe so, in the same way if a fast food chain is offering a prize of a million dollars to some lucky person who buys, for example, the thousandth whopper, they must have the money to back it up

Most companies do not lie about charitable contributions. Charities report their donations as part of their non-profit status so you can check even on private companies.