Ethical risks

Hello sir. I would like to ask if a company is listed, is it allowed to an audit firm to supply other services when it has also the audit engagement? And also in BPP there is an example which does not provide which threat is that (self interest???). Salt & Pepper guarantees that its audits will not last longer than two weeks. The amount of time required to complete an audit depends upon the nature of each audit client's business and the level of associated risk. To restrict the duration of all audits to two weeks, regardless of the level of complexity and risks of the business, will result in sufficient and appropriate audit evidence not being obtained. Salt & Pepper would be at risk of giving incorrect audit opinions, leading to possible litigation. The firm would contravene the ACCA Code of Ethics. Thank you very much.