Does Western Union there report it to the tax service?
No. No problem. Western Union only know the name (and will need to see the person's ID) but they don't report anything to the tax office unless they are told to.
The person collecting the money will need to give the amount (and what currency it's in), the control number your name and the country you're sending it from. No address is necessary in Poland. They will of course record the person's ID number when collecting the money.
And if so what are the triggering amounts that would cause them problems?
If it was a bank, 15000 Euros would be the triggering amount. Western Union probably have to follow that rule, however I used them the other day to send something to Poland and I don't remember their website mentioning it.
Like is there a limit or number of transfers that would have them flagged for being checked up on?
See above. If the person collects the money from a branch of a bank that has Western Union facilities, that bank might have their own rules about payments. How much were you thinking of sending?
I am not sure how a money transfer is considered by the Polish tax service...if its income etc and is reported by the Western Union or bank to the government.
In theory gifts should be declared by the recipient (as Sa11y says, the darowizna rule allows smaller ones to be tax free under some circumstances) however declaring gifts is the personal duty of the recipient when they fill in their tax return. Sending by Western Union should be OK and you shouldn't worry.
I never understood why anyone would use Western Union for money transfers.. Their prices are extortionate compared to most banks..
Speed and relative privacy. And actually not extortionate if you're in certain countries where Western Union is cheaper than the banks. Or if your bank isn't a correspondent bank to the one you're sending to. Plus of course the contents of a Polish bank account are not
private, and if the person owes some money to the state (for example ZUS) their bank account may be frozen.