Simple question. Do you ever ask your client to make the approach to the link propspect? And if not, why not?
There are times when that high quality link prospect will clearly respond better to an approach from your client, rather than from an SEO/link builder. If your client is an expert in their field or holds some credibility/trust etc in that particular field (same as link prospect) then surely an approach from them will get a much more favourable response than from an SEO/link builder.