In my experience, terms with lots of if-then conditionals are the most common flag. The last "messy" term sheet I saw had an unusually long diligence period. Predictably, the investor "found" a bunch of problems at the 11th hour and pulled out, leaving the startup in a financial lurch.
Anything that differs from standard docs should be _highly_ suspect, assuming you can get ahold of some.
As a lower bound, I've never seen terms presented on Shark Tank that weren't off-the-wall insane. :D
> How would a first time founder tell the difference?
By talking to other founders, advisors, and their attorneys. This book was useful when I was approaching the first term sheets I ever saw: http://www.amazon.com/Term-Sheets-Valuations-Intricacies-Big...
http://www.amazon.com/Mastering-VC-Game-Venture-Start-up/dp/...
http://www.amazon.com/The-Startup-Game-Partnership-Entrepren...
http://www.amazon.com/Term-Sheets-Valuations-Intricacies-Big...
http://www.amazon.com/Venture-Capitalists-Work-Billion-Dolla...
http://www.amazon.com/Raising-Venture-Capital-Serious-Entrep...
http://www.amazon.com/The-Art-Start-Time-Tested-Battle-Harde...
I believe any one or more of those will get you going in the right direction. All of those I've either read, or have seen recommended highly enough by people I trust, that I feel comfortable recommending them. The Guy Kawasaki book is a good, basic introduction to starting a startup, although it's a little old now. I think most of it is still relevant though.
A lot of this stuff is probably on the 'net as well, but you may have to dig around for it a bit. Quora has a lot of good questions (and good answers) on VC / startup topics, so that might be worth a look. Also, a number of high profile VCs maintain blogs where they share a lot of useful information. Mark Suster comes to mind (http://www.bothsidesofthetable.com/) and does Brad Feld (http://www.feld.com/wp/). Note that Brad Feld is the author of one of the above books.
https://www.amazon.com/Term-Sheets-Valuations-Intricacies-Bi...
https://www.amazon.com/Venture-Deals-Smarter-Lawyer-Capitali...