It may seem like a good idea to pay someone to publish your poems but it is not necessary.
I am mainly talking about certain small advertisements that promise publication - and this applies to books as well as poems.
The BBC TV show "Bookworm" even proved how poor some of these publishers are - a poem made of random words from a telephone directory was accepted for publication.
My advice? If you are asked to pay more than £20 for a single copy of the book containing your poem, then it is not worth it.