In the market for….

I'm not sure there is such a thing as a
"good ROI sites to find used motorhomes??"
I would say look in Europe France, Germany.

Consider what you want, who is travelling in it. A class, B class or Van conversion, could you deal with Left Hand Drive

Here just Google Motorhomes for sale, then whittle down to the price you have in mind, if you see something you like, bring the details back here and ask the advise about it. There is a lot of experience with different Motorhomes on here.

I wouldn't necessarily criticise any of the Irish dealers, for their customer or after sales service. That said I have never bought from them, but I have found their product support Lacking, also their prices are Grossly inflated, ask anyone who has had the unfortunate ecperince of asking for a valuation for something they bought in good faith from them.
Unfortunately in this country very few have any idea what a reasonable and fair, profit margin is.
As one of my past Bosses like to quote, "the custom is King, F##k Him " and he had a poster on the back of the sales office door to remind people.

I would also say look at the for sale section here,great thing about it is that you know where it came from and available to answer any questions