INT has a higher precedence than string, the string will convert to int, so if that is an int column (which we don't know), then the query will be essentially

SELECT @ProductID= ProductID FROM Product WITH (NOLOCK) WHERE SalesID= CONVERT_IMPLICIT(INT, '@salesId') and Product = 'Clothes '

Which is SARGable and going to fail with a conversion error.

If you don't believe me, try running this:

IF ('This is a string' = 1)

print 'True'