Many of those types of requests are done with bots or automated software, most times the person never even sees your site anyways. How can that be quality link building. Course think you have your answer already anyways..
Ya the mainstream ones can be a stupid, again because they harvest link trades. Had one, they sold baby clothing and related and they were linking to adult sites, how smart is that.
Sounds like you would'nt have gotten much from the trade anyhow.
ronnie