You should almost always avoid working for low-margin businesses. Sure, if they are new and growing, there's an exception, but if their whole growth plan is premised around being low-margin, it's not going to be a great place to work and advance your career. Expenses such as compensation are always on management's radar.
It's pretty well known around Seattle that Amazon pays their employees very well, and has a tendency of giving ridiculous signing bonuses.
Here are salaries at glassdoor. Nothing amazing here: http://www.glassdoor.com/Salary/Amazon-com-Software-Engineer...