As a member of the Society for Editors and Proofreaders (SfEP), PlainPaperPublishing abide by their Code of Practice (CoP). The CoP is endorsed by the SfEP council. Although it isn't a legal document, it's considered binding on members, associates and corporate subscribers.
The SfEP's code of practice (CoP), Ensuring editorial excellence, is a really useful resource for editorial workers – editors, proofreaders and project managers, whether working freelance or in-house – and their clients and employers. Its purpose is to establish standards of best practice for SfEP members and associates and help them maintain them and to encourage good professional relationships.
Good communication between client/employer and freelance/employee is essential. Clear briefing and the agreement of terms are vital if high standards are to be maintained by both parties, and unsurprisingly they're emphasised by the CoP.
In addition, the CoP includes guidance on: the professional behaviour of both freelance/employee and client/employer; standards for proofreading, editing and project management; and information on web editing, electronic file handling, email etiquette, confidentiality and computer security.