What tool do you use to establish search volume? It seems impossible to get anywhere near an accurate estimate. Example: if you take the term "travel to europe" according to the google keywords tool there are 2400 searches globally per month currently (first point - I think this is impossibly low) but according to a Moz tool there were 53,000 global searches on Bing alone and according to an overseas agency we used the google keywords tool shows 673000 global searches for that term So how can you plan without knowing the search volume?
You can use Keyword Planner to search the Global Searches of your keywords to find some reliable searches.
I found the Google Keywords tool, whilst not always accurate, would usually give a good estimate on the amount of traffic a keyword receives, and if it's worth pursuing or not...
Think you kind of answered the question yourself, if something doesn't look quite right, check it with as many other keyword tools as possible to try and get a more accurate number. Best you can do.
You are probably using the Broad Term and not Exact. If you also choose a particular country against worldwide your result will always be different.
Well first of all, global monthly searches refers to searches from all countries in all languages, you also need to ensure ''exact match'' is selected. The keyword tool is actually quite confusing to get data from, thankfully, the new keyword planner which has replaced it will give you much more accurate data and you don't need to worry about local or global.
Stop worrying so much about search volume. You'll still get traffic from terms closely related to your terms, so either way you're gonna get plenty of longtail traffic. Think "big picture" not just strictly the kewyords you choose.
I use Rank Tracker to check rankings http://www.seopowersuite.com/rank-tracker/, and sometimes I research keywords with it. It takes data from the new Keyword Planner and so far the stats have been accurate, at least on the occasions when I double-checked. But you gotta make sure the settings are the same as your settings in Keyword Planner.