Ah. Okay, you should probably use sheet.cell_value() for individual cells. This should pare you down to just the unicode string.
EDIT: Looking through some of code used here, you may not have to change to cell_value. Read on for datatype matching, though.
Also, be sure that the value of the tag you’re reading is also a string, or converted to one at some point. The data types will need to match when you compare them.