The listings that get on trulia, get pulled in most cases automatically from the MLS.
I don't think individuals can post listings on the site.
If you are worried about if offers are valid or not, we need to get you in touch with a realtor to help you work through the process. It's a great question...with lots of details and expertise needed to evaluate. How much earnest money, how much option, what lender, what title company, how fast can they close, what type of financing they're using, does your home qualify for the financing they're using, does the down payment match the type of financing they're using....and 100s of other details.
No web site can probably walk you through the steps of all that unfortunately.
If you need a referral to a great realtor in your area, just drop me a line.