I suspect I know what your problem is, but lets leave that for a moment, and fix a much more important problem first: Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.
When you concatenate strings, you cause problems because SQL receives commands like:
SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'
The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:
SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;
Which SQL sees as three separate commands:
SELECT * FROM MyTable WHERE StreetAddress = 'x';
A perfectly valid SELECT
DROP TABLE MyTable;
A perfectly valid "delete the table" command
And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.
So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?
FIx that throughout your whole app right now, and make sure you don't miss a single case - or your best mate will destroy your DB just to see the look on your face ...
Then change your DB design. I'm guessing that all the fields in your table are VARCHAR or NVARCHAR from the passing of a textbox content as the Rate to check - that's bad and causes a problem for you because all string based comparisons are made based solely on the first different pair of characters encountered.#
Which means that "1000.0" is smaller that "9.7" because the first different character pair is '1' and '9', and '1' is less than '9'.
I'd also expand your table by replacing the Weight column by two columns: MinWeight and MaxWeight - which means that the comparison doesn't need anything more than
... WHERE @Weight BETWEEN MinWeight AND MaxWeight ...
Which makes life a whole load easier!