Before anything: Maybe I've not explained adequately: There's a need of a substitution and the one that is going to pay is a PRIVATE that already works as QA Game Tester for a Company (that is not play2.it - that is a non-profit project - we are just friends).
He's actually in need since he's at the hospital and he wants to conclude a specific task (no matter the company that he works for). This post is not about "arguing" but I try to reply in the best way that I can.

"18 Europe currency for an hour is not going to get you a professional when   the same job offerings are over  30 to hire a professional plus with benefits too"

1) Name your price, that's what usually professionals do. Note that there's a ~ (tilde ) near the 18€ (net), that means approximately. You need also to add the taxes, etc that cannot be presumed since we are in an international market (check also point 2).
Anyway the current (Average) hourly pay for long term hired professionals is lower than 18€ (gross - that means in ).

The current market is telling something different and even the same person in need does not gain what you are supposing. But there's no problem and no will to argue about the costs (name your price).

https://www.gameindustrycareerguide.com/video-game-tester-salary/

"Then looking at your website you don't have VAT to conduct business since you will have to pay taxes for it."

2) The website is Totally unrelated! I'm NOT the one that is hiring.
Even if the website is unrelated, even if it's a non-profit project (Again: not related to this post!), it has a VAT nr (related to another company) to satisfy local rules in italy.
The one that is paying is a different subject.
There's no need to argue about it.

Depending on the country the taxes are up to the one that is receiving the payment. Since we are on an international market it's impossible to predict which taxes the receiving side is going to pay.

"This also goes into question on how will you pay, you normally pay by paypal i assumed since many smaller business do but a professional would like to do it professionally and get it by bank ACH or IBAN/SWIFT/BIC."

3) I'm NOT the one that is paying you (read again the post) and I don't the payment method that you are going to use.
The payment method is totally indifferent and makes no sense to suppose that a bank transfer is more or less professional than paypal. It makes no difference.
For sure you (whoever) could be paid with any preferred (most common) payment method. What I know (since I already know that he uses them) is that there's no problem for both bank transfer or paypal.

"You be paying  648,  you need to do this to avoid cost."

4) I don't know what is that 648. What costs are you referring to? If it's about paypal (that you introduced as payment method) we don't care about those marginal costs and It's more than obvious that they can be agreed before going ahead (not with me but with the counterpart that is paying).
That's not an issue and there's no need to argue about it.

"Just saying that if you going to be asking for a professional, you may want to actually be ready for one"

5) I don't know ... a professional usually shows what he can do, names his price, makes his own agreements and try to conclude every aspect. Taxes management is up to him (as for the counterpart for his own taxes).

I'm sorry but the work was already started a bunch of days after the post.
You can still send an email (check all the post above) with all the info in order to be added into an address book and called in case of need.

Kind Regards