Re: What are the odds of a DNA match with someone else.

The answer to your question is " it depends". It depends upon the
way the DNA samples are analyzed to determine relatedness.

The real answer is that DNA from different individuals absolutely are
different. There is no doubt of that. The only exception being identical
twins whose DNA is identical.

Now the problem that arises is how much effort is expended (or what tests
are run) to determine whether samples match or not. It would be impossible
to completely characterized the entire DNA content of an individual. 
That would take 10-20 years with current technology and cost hundreds of 
millions of dollars. So people who do DNA testing take shortcuts and do
much simpler tests to determine relatedness. There are different tests
that can be run, and each has a different probability. So I can't give you
an actual number. But standard testing from a competent lab will produce
odds that finding two samples that appear to match are in fact from the 
same individual with the liklihood of an accidental match around 
hundreds of thousands to millions to 1.

Now these numbers are tricky, because they look at the whole population.
However if you have a number of individuals from some subpopulation, then
you need to reinterpret the numbers. For example if you had an individual
from some genetic subpopulation then their DNA would likely be more closely
related to other similar individuals. Hence the likelihood of an error
is much higher if the population is not random but skewed in some direction.