I know a lot of people find the current production Dovo great, and I must say you're lucky because these are plentiful and inexpensive (almost any vintage razor costs more in brand new condition).
I don't consider them great razors by any stretch of imagination. Now the vintage Dovos are a different story, and I don't know why the current production is not on par with them.
Perhaps this is just my subjective evaluation, but if you look at the razors I have you'll know I'm not making it up.
Now on vendors taking back razors for 'any' reason - this is just not true. Yes, they will go a long way to make their customers happy, but that's not even close to say 'Satisfaction guaranteed, or your money back' policy. A policy of this kind adds a large overhead to the cost of doing business. I don't want to turn this into another economic discussion, but it's good to stick to the facts - some things are just unfeasible.
There is a big advantage to purchasing a new Dovo and it's consistency. It may not be the greatest razor ever made, but there is plenty of people who have shaved with one of those, and unless you are a special exception you should be able to get a good shave with it as well.
The bottom line is it's not all that difficult and Glen summed it up quite well. Figure out your parameters and go find something that fits in there.