PWN is peer-to-peer, meaning users agree on the loan terms between themselves. As a lender, your rate of return will be determined by your ability to find borrowers in need of what you have.
Depending on various factors, including the collateral type, duration, and potentially even the borrower's PWN history, a high or low APR may make sense to a lender.
There is no maximum or minimum APR per loan, although in a dense marketplace, you may find competition when demanding outlandishly high return rates from borrowers.
The worth of the collateral for a loan is determined by outside research, using third-party pricing sources. For ERC-20 tokens, this is commonly done on sites like coinmarketcap.com. NFTs can take a bit more research and knowledge of the specific project, but research can include sale prices of similar assets on OpenSea.
Offers cannot be edited, but they can be cancelled with an on-chain transaction by the lender. You may also create as many different offers as you would like on the same loan for free, at various token types, duration, and APR. However, keep in mind that offers are made to an asset, not to a loan request. All your signed offers are valid until cancelled by an on-chain transaction or accepted by a borrower. If a borrower accepts a different offer, they will be able to accept yours after repaying the current.