Temp Offer Advice

I typically focus on permanent recruitment, but I’m seeking clarification on handling temporary roles.

I have a client ready to offer a day rate for a position and they’re inquiring about the candidate’s expected rate.

When discussing the candidate’s expectations, should I include my desired margin percentage? For example, if the candidate expects £500 per day and I need a 20% margin, would it make sense to quote the client a rate of £600?

Additionally, should I inform the client that this figure includes my fees, or simply present the rate of £600 without further context?

Is a 20% margin considered too high? Have others experienced situations where clients revoked offers due to the margin fees being perceived as excessive?