You're just a designer. As long as you aren't designing them a logo where YOU blatantly rip off someone Else's copywritten/trademarked design you should be fine.
Gary
This may not be true, you are in fact, now, knowingly designing something that Canadian company "MAY" have a legal trademark for the name "LUCKY 7"
I would discuss this with a lawyer, being paid 3 times more may not cover the 10-100k costs... unless you are getting paid 33k for the logo design, in that case you are on the wrong forum.
We also have a clothing company here in the states called "Lucky 13" and I believe they have a registered trademark for clothing (
http://www.lucky13apparel.com/)
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On the design, you should have researched "LUCKY 7" or anything dealing with that, you would have found the competition and gotten some visual cues. One thing that sticks out to me is, what kind of crowd or culture are you designing too? The 2 examples are miles apart in culture, the Canadian Lucky 7 is sleaze/maxi-clip-art fluff done a million times. The other rockabilly/retro with original artwork.
Can't crit the logo if we don't know the crowd you are designing too...
You might want to check out the MAGIC and ASR organization websites for trades hows to attend if you are interested in ths type of work, but beware, it is over saturated and pays very little.