I cannot help you with the Laryngotracheitis question, but I can tell you based on what I have learned about Marek's disease, I would never purchase birds or bring them in from a flock that has had confirmed Marek's within the last decade.
As someone that has had a bird die from this disease, and now my entire flock are 'carriers', I would not wish Marek's on an enemy! There is no cure and it is truly sad to see a bird go through it. Even if I were to breed and vaccinate for resistance in my flock, I would never with a clear conscience sell my birds, even many years from now.
Marek's is a virulent herpesvirus and can live in an environment for years. If this fellow truly had Marek's disease on his property, in his flock, before... he still has it. The only way I can think of that he'd be rid of it is if he culled the flock that had it, completely sanitized every square inch of coop(s), and waited many years before bringing chickens in again. It is shed in the dander of infected birds (even if they do not become symptomatic). It is entirely likely that his birds are still carriers, and never show symptoms because they are vaccinated. They may also have, over the years, built up some natural immunity as well.
You can buy the vaccine and vaccinate your current birds. This may help them, but please be aware that the vaccine is only at its most effective when administered to day-old chicks, so that they can build resistance as they mature. Vaccinating your adult birds now, as an analogy, is NOT the same as vaccinating an adult dog for something like rabies. The vaccine does not cause immunity-- rather, it works with the chick's natural immune system and builds a resistance. This is about 90% effective when HVT (Turkey Marek's) vaccine is administered to day-old chicks, against Marek's. However, there are now mutations of the Marek's virus out there, and so there are a lot more variables at play. HVT is proving somewhat ineffective against some of the other Marek's strains.
In a nutshell:
-The birds from a past Maerk's positive flock are possibly carriers still.
-If you bring in carriers, they will still shed small amounts of live Marek's herpesvirus and it is very contagious.
-Marek's is very virulent and can be 80% or higher lethality in chickens that do not have resistance/immunity.
-You can vaccinate your adult birds and it will not HARM them but it may not help them against Marek's. It is a big risk.
I would personally seek my bantam cochins elsewhere, however the choice is yours! You may not have a single problem, or it could be a nightmare. If you are very set on getting the birds, you might ask some of his past customers and see if they have had any illness or unexplained deaths in their flocks.
I'm not trying to scare you-- I'd just hate for you to knowingly bring this disease home! Once you have it, you are married to it, so to speak.
