I use a Bayesian-script for spam-protection and it works quite well, but the technology behind it does not seem particularly suited for predicting price changes.

In my Encyclopedia Britannica I read

Bayesian estimation: statistical technique for calculating the probability of the validity of a proposition on the basis of a prior estimate of its probability and new relevant evidence.

Also note that Bayesian analysis is very sensitive to the distribution of the input. The best you can hope for is to code all relevant input parameters (and until now nobody has been able to identify all parameters which govern price-changes) and the resulting price-change (increase, stable, decrease), so as to validate the probability of a proposition that a new set of input data will lead to a lower, higher or stable price.

Its predictive power will be minimal I fear, even with full knowledge of all relevant data.

CountZero

"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law