How to see the value of a variable being used in an sql statement during a server trace?
For debugging purposes you can trace them explicitly into the Profiler using a custom event, via sp_trace_generateevent:

declare @tracedata varbinary(8000);
set @tracedata = cast(@transferdate as varbinary(8000));
exec sp_trace_generateevent 82, 
        N'@transferdate', 
        @tracedata );
set @tracedata = cast(@oldcust_id as varbinary(8000));
exec sp_trace_generateevent 82, 
        N'@oldcust_id', 
        @tracedata);


You need to modify your Profiler session to monitor for the user User-Configurable Event Class, otherwise you won't see the generated events. I would also comment out the call to sp_trace_generateevent in production once the debugging is done. The call is not critically expensive (specially if there is no monitoring listening for it), but it should be removed none-the-less.

Updated

The exec call doe snot allow for a CAST to be inlined in the parameter list. I modified the code to show how to cast it before the exec. The value will be in the BinaryData column, in HEX representation (so 'daf' will show up as 0x646166).