Need help developing web service that grabs data from CommerceServer 2007-Collection of common programming errors

For this scenario, you might consider using BizTalk.  Commerce Server ships with a set of these, and there are also adapters for SAP.  They’re reliable and tested, and they don’t require you to roll your own web services as well.  But if you do choose to roll your own, use the web service methods, and not direct SQL.