Hello Mark,
Thanks a lot for your help.
I understand that I can define the field which blocks update via admin section.
What I still don't understand is how it works when Marketo and Salesforce both have a value on the same field, and this field doesn't block update. Do you know what's the rule in that case? "Salesforce always win" , "The newer value always win" or "Neither of them is updated"?
I hope to hear from you again soon, or someone can help me find out.
Thank you very much.