In Jane Austen's Pride and Prejudice, Lydia's reputation, caused by her behavior, is the clearest example of how reputation affects courtship and marriage prospects. Lydia's poor behavior is evident from the very beginning of the novel. For instance, when Lydia and Kitty begin frequenting Meryton in pursuit of flirting with soldiers, Mr. Bennet refers to them as the silliest girls in the country (Ch. 7, Vol. 1). She is even seen flirting with Wickham while playing cards at the Philipses' (Ch. 16, Vol.1). Even before Lydia runs off with Wickham, her behavior threatens her other sisters' prospects. We see this in Darcy's letter to Elizabeth when he mentions the impropriety of her family, we also see it when Lydia is invited to Brighton and Elizabeth tries to persuade her father not to let her go. Elizabeth argues that her father would not permit Lydia to go if he "were aware...of the great disadvantage to us all, which must arise from the public notice of Lydia's unguarded and imprudent manner; nay, which has already arisin from it, I am sure that you would judge differently in the affair" (Ch. 18, Vol. 2). Elizabeth is of course referring to the behavior Darcy speaks of in his letter which led to his own hesitation in asking Elizabeth to marry him, but also led to his convincing Bingley not to pursue Jane further. Hence, Lydia's flirtatious behavior affected her two eldest sisters' courtship and marriage prospects.
When Lydia does run off with Wickham, Mr. Collins takes the time to write a condolence letter informing them that "this false step in one daughter will be injurious to the fortunes of all the others" (Ch. 6, Vol. 3). In other words, Lydia's elopement has ruined marriage prospects for all of the daughters. It was only by virtue of the fact that Mr. Darcy forced the marriage that their reputations were saved.
Other, smaller instances of reputation can be seen in Mrs. Bennet's behavior. At the Netherfield ball, Mrs. Bennet makes some very serious social faux pas, including talking about Bingley and Jane's wedding prospect, there at Bingley's dining room table, well before he has even proposed. Her behavior is reproachable and as a result, Bingley's sisters and Darcy persuade him not to propose. Hence, Mrs. Bennet's behavior undermined the reputation of the entire Bennet family and ruined the daughters' courtship and marriage prospects.