Is oanda.com data trustworthy?

Yes, OandA data are trustworthy. They are very careful in capturing all
the data they can (that's a lot!) and processing it very carefully. But
you have to read carefully what they are telling you about the numbers
you are seeing! :-) (Read An Introduction to High-Frequency Finance by
Michel Dacorogna, et al., to get an idea.)

The big things to look for in treating OTC markets are timing, source,
and price type. OandA, the US Fed, and the Bank of England (or any other
source you have) give data for different times, different sources, and
different "averages". Many researchers try to focus on a single-point
source (say Reuters or Bloomberg feed) so the data are timestamped
consistently, pick a particular time (say London 10 am or NY 2 pm), and
quite often use just bid prices (or both bid and ask.) Any averaging
across time or prices (like mid) changes the statistics, but if you know
what you are dealing with, you can probably take it into account, at
least partially, and it may make for smoother data series.

and just to rag on it again, EUR/USD is the number of US dollars per
Euro, the usual way of quoting this pair, currently around 1.1700 .

David L. Reiner
Rho Trading