How to tell if the logos really are that similar
Chances are if you're looking at this post, they are. But here are some tests you can try:
- Making them both grey-scale.
- Viewing them from far away (or very small versions).
Are they even more similar with any of these variations, possibly including combining them? If so, the logos are probably too similar.
However, basic shapes are just that - basic and are used in composition to create more complex things, so if they're similar it's not as big of a deal. For example, Scott Hanselman points out in a blog post there's only one cloud icon. Basic shapes are okay to use across different logos. If the logos are both complex and similar, you'll have a lot more reason to be concerned.
Are these logos too similar?
From a legal perspective
Based on this post, if you can distinguish between the logos when they are side by side and the logos don't look like newer/older versions of each other, you should be alright.
This is especially true if there's clearly no attempt at intentionally misleading consumers and the companies are not competing for the same market. There are several big name companies that have similar logos, but since they're in different markets than each other it's alright. Note that this is similar to how color copyright works.
Plagiarism is taking another's work and trying to pass it off as your own, which is always illegal as far as I know. Based on your description, that hasn't happened in this case.
Note that I am not a lawyer, nor do I know what the ruling in your jurisdiction is regarding this topic. This post has no legal authority regarding whether you can use the logo you've created. For true legal advice,
hire a lawyer in your area.
But the question is should you, even if it is legal?
From a branding perspective
Do you really want the logo you made looking like another company's? Does the company really want people to have a chance at getting your company confused with another? The answer to that really should be no, especially if that other company is in the same or a similar market as the company that you made the logo for.
But even if the companies are in different markets, what feeling or connotation does it give off? Is that feeling or connotation really want you want when people see the logo you made?
From a design perspective
Are you really happy with designing something that looks almost exactly like another's work? It's your duty to push forward and be innovative while still completing the job you were hired for.
How to approach this topic with a client
If you really think the logo is too similar to another, you need to tell the client about it. Most likely the client will not be happy that the logo you created is similar to another company, especially if they're happy with the logo, but you've got to talk to them about it anyway. Explain to them that it would be far worse to get sued or to have consumers be confused. It's in everyone's best interest to change it.
As for pricing, that's really up to you. You could charge for more or not depending on how guilty you feel. Hopefully you created some other variations that you can pursue or can come up with a way to change this variation to make this logo distinct from the other company's.
How to change the logo to make it more different
Here are some guidelines for changing a logo that's similar to another in order to make it more different:
This is, of course, in addition to guidelines of creating a good logo in the first place.