How does Austen's tone convey her criticism of marriage in Pride and Prejudice? Please give quotes to help explain.

Jane's sarcastic witticism is what makes her convey her
personal views of marriage as a tool to create status instead of as a symbol of love.
Granted, Jane DOES understand that marriage SHOULD be a symbol of love, but she also
admits that this view is not accepted within her current
society.

Some of those phrases come from Charlotte,
especially who is the first to admit that she would marry Collins  only to be safe and
have a place to live:

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"My reasons for marrying are, first, that I
think it ... a right thing for every clergyman in easy circumstances (like myself) to
set the example of matrimony in his parish; secondly, that I am convinced that it will
add very greatly to my happiness; and thirdly--which perhaps I ought to have mentioned
earlier, that it is the particular advice and recommendation of the very noble lady whom
I have the honour of calling
patroness."

This shows you
the sadness of Charlotte's situation.

Another of many
quotes is

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"Pardon me for interrupting you, madam," cried
Mr. Collins; "but ... if she is really headstrong and foolish, I know not whether she
would altogether be a very desirable wife to a man in my situation, who naturally looks
for happiness in the marriage state. If therefore she actually persists in rejecting my
suit, perhaps it were better not to force her into accepting me, because if liable to
such defects of temper, she could not contribute much to my felicity."
(1.20.4)

In this quote,
Collins is clearly assigning a status to women as many other men did at the time and
warning Mrs Bennet about Elizabeth's behavior as being dangerous for marriage, due to
her open mindness and ouvert communication.]

This next
quote, however, hits marriage hardest and again comes into Charlotte's choice for
marriage over poverty, and here is when we hear Jane, and not Charlotte's mind,
speak:

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Charlotte herself was tolerably composed. She
had gained her point, ... and had time to consider of it. Her reflections were in
general satisfactory. Mr. Collins, to be sure, was neither sensible nor agreeable; his
society was irksome, and his attachment to her must be imaginary. But still he would be
her husband. Without thinking highly either of men or matrimony, marriage had always
been her object; it was the only provision for well-educated young women of small
fortune, and however uncertain of giving happiness, must be their pleasantest
preservative from want. This preservative she had now obtained; and at the age of
twenty-seven, without having ever been handsome, she felt all the good luck of it. The
least agreeable circumstance in the business was the surprise it must occasion to
Elizabeth Bennet, whose friendship she valued beyond that of any other person. Elizabeth
would wonder, and probably would blame her; and though her resolution was not to be
shaken, her feelings must be hurt by such a disapprobation. She resolved to give her the
information herself, and therefore charged Mr. Collins, when he returned to Longbourn to
dinner, to drop no hint of what had passed before any of the family. A promise of
secrecy was of course very dutifully given, but it could not be kept without difficulty;
for the curiosity excited by his long absence burst forth in such very direct questions
on his return as required some ingenuity to evade, and he was at the same time
exercising great self-denial, for he was longing to publish his prosperous love.
(1.22.3)