Like many other ebayers, I have been very happily buying and selling Dublo, Triang, Wrenn etc model trains for longer than I care to mention. I've been conned on more than one occasion. I hope that this will help others not to be (or at least feel as if they have).
Firstly I never cease to be amazed at the number of people who expect 50 year old model trains to work straight from storage as well as they did, well, 50 years ago and who get upset when this doesn't happen!! Where Dublo is concerned I always expect to have to spend a few bob on brushes and springs, pick up shoes etc, and frankly don't begrudge £20 or so on a complete service/motor remag if the model is in nice condition. In the past I have used the services of Scalespeed and the improvement in performance has on each occasion been phenomenal. Don't penny pinch and you'll be really pleasantly surprised. There is (contrary to what the super neo magnet brigade say) absolutely no substitute for a full service by a professional technician. Dublo is very restorable if you do it properly. Don't forget that in times gone most locos were returned to the factory for this service although some dealers did the job at their shop. There is really nothing sadder than to see a Dublo layout at a model railway show with locos struggling round with 3 coaches, all for the want of a little TLC and very modest expenditure.
Secondly, establish links with other collectors and join the HRCA. Great organisation and an absolute goldmine of information and elusive spares and the above mentioned experts. You won't believe their spares directory!!! Again, a bit of an outlay but it really is a case of penny wise............
Finally, don't forget that most ebay folk really are honest citizens - rogues soon get found out - but simply dont know what they are talking about ( just like some dealers!!!) Be patient, prepare for the odd upset but above all persevere. Don't accumulate too many bedraggled 'bargains' as frankly they're not worth it and will just clutter up the train room (been there, done that, got all the bits.) A few nice pieces in tip top mechanical condition are in my humble opinion the way to true satisfaction.
And oh yes, don't take it too seriously, just ENJOY YOURSELF!!!!