1. If you have no sample, skew your proposals towards your certification and courses. For example, I have a certification in Content Strategy. Telling the client of this and what I learnt during my certification might suffice.
2. The assignments you did during your training can be presented as sample.
3. If you worked in a team on a writing project, you can share that as sample and tell the client of your involvement. Get permission of client and team lead.
(On your second question, it’s part of the topics I will discuss on my YouTube channel, subscribe: https://www.youtube.com/channel/UCBtepvre3ERD-hG7f-dSL0Q?sub_confirmation=1