When starting out as a quasi-amateur/professional photographer its very tempting to say yes to almost every request placed before you. The glimmer of getting one's name and photos out into the "real world" is pretty enticing. Its easy to sell oneself short thinking thoughts like these...
"well, I'm not well known..."
"I don't do this as my career"
"I have to get my work out there some how if I'm going to go far."
You get the idea. While each statement holds a tiny bit of truth the reality is that even the most amateur photographer needs to hold some pride in their work and themselves. There are offers that can be refused and there are prices you can stick firm to.
Often I get emails asking to use my photos for one thing or another. This presented a couple of challenges for me... what in the world should I ask for a price, and what should I ask for in return or as stipulation for use of a photo? While there are no set prices for photo use and you really need to feel out what the person making the offer is willing to pay there is one aspect I refuse to bend on.
Giving credit where credit is due.
No matter how enticing an offer is you need to make sure that someway, somehow your photograph will be used in a way where it is credited to you as the photographer. What most photographers do is art, not stock imagery. If someone ever offers you to pay you for your image, but not necessarily give you credit do not accept the offer unless you are prepared to give up total rights to your work. Lack of credit leads to anonymity. While being anonymous doesn't bother everyone I highly stress for every fledgling photographer to avoid it.
You're worth a byline for your work, no matter what its used for.