I assume you mean that the prospective renter can afford it.
Unless the price is raised for all renters and is so announced, it wouldn't be ethical to raise it for just one applicant. Adjusting the price for other factors could be legitimate, such as pets or not, services supplied like lawn or pool, and so on.
If you have advertised the price, you should be willing to stand behind your advertisement. You might get some pushback from regulators for not adhering to an offered price.
You could withdraw the advertised price from the market, and then re-price it. But that seems somewhat inconvenient.
Consider consulting an attorney if you're thinking of being arbitrary with pricing. But as Realtors, we should try to avoid any question of ethics and putting the client in a position of having to defend his agent.