Quote, purchase order and legal contracts

Hi, We are a small start-up, and we are trying to sell software to some big corporations. The software is sold for less than $3K and several staff members of the companies want to avoid their legal department. Here is the common situation that I have experienced, and I would like to know if I am taking a big risk accepting this way to proceed: The company ask for a quote, but they do not want us to leave a line for them to sign. They will create a purchase order, but they will never sign the terms and conditions or a contract, and they expect me to sign it. In the quote I add a line that says, " all services are provided under my company terms and conditions". The software is re-distribute with a license, so if after a year they do not pay the license will expire and they will not longer be able to use it. The question is that if I sell the software just signing the purchase order, is there any danger for my business that I give them some rights? Thanks