Belgian Citizenship

My South African friend got his nationality without involving a lawyer. I also got it without involving a lawyer.
It's quite a straightforward process so you either fit all the criteria necessary to obtain it or you don't.

Agreed that in case is rejected a lawyer can appeal but beforehand I am not sure they can provide any additional help.

However you could try with www.allrights.be and they can evaluate if you fit all the criteria. There is also an online tool (Schéma interactif) to test it yourself

The Belgians won't be at all concerned as to whether you retain your South African citizenship (unlike, say, the Netherlands). The document that confirms your Belgian citizenship will be headed "change of nationality" (in French, Dutch or German according to where you are domiciled) but that merely reflects the fact that as far as the Belgians are concerned you will be Belgian and not a foreigner living in Belgium.
It may, or may not, be the case that the South Africans require you to relinquish their nationality once you have become a citizen of another country but that would have nothing to do with Belgium (and no doubt you have checked the situation vis-à-vis South Africa already).
Money spent on a lawyer here would be totally wasted - if you are that well off, you could give it to a charity instead. If you are still worried you could ask a notaire/notaris for advice, their ADVICE comes free.

As noted, the Belgians really don't care if you have dual nationality. If you still feel that you need legal advice, you should speak to a South African lawyer who specializes in nationality and immigration matters in South Africa.

Also, as much as I agree with BECASSE on many issues, the idea that notaire's go around handing out free advice (especially on matters in which they have no qualifications, training or jurisdiction) is pie in the sky.

Notaires provide legal services and advice in some very limited areas of civil and commercial law, such as the purchase and sale of real estate and real assets, family law, (marriage, divorce, inheritance etc.) and company law, such as the registration and formation of companies.

There isn't a single notaire in the country who will give you free advice on nationality matters.

'There isn't a single notaire in the country who will give you free advice on nationality matters.'

Well ours did!

Maybe because he had dealt with us on a wide range of matters from buying and selling property and drawing up a pre-nup. And maybe because it was just a simple case of confirming that the Belgians have no problem with dual nationality and are not going to contact another country to tell them that Joe Blow has just become a Belgian. Nevertheless, I got the advice that I wanted before becoming a Belgian and there was no charge.
By all means ask a notaris; they can only say that they can't help you.

I didn't need to ask my notaire in respect of a nationality application because I had read the appropriate part of Belgian law and that law was quite clear (as the Directrice Generale of my commune agreed when I pointed out the relevant section to her). Nevertheless, my notaire had previously made it more than clear that he was prepared to give free advice on matters of administrative law such as nationality. One advantage of a legal system based on codified (as opposed to case) law is that one only has to read it to know what the law says - and a notaries' training certainly fits them for that task.

It's irrelevant if someone is highly skilled or not, that is not how Belgian nationality (declaration) law is, it's based on contributions to society in terms of social, financial participation. I'm sure if they are so skilled, they don't need a colleague asking about lawyers on an internet forum on their behalf but are capable of googling "belgian nationality" which will lead to several informative websites.