Why is bartering uncommon in modern countries? Recently, I witnessed two acquaintances of mine engaging in bartering, where one traded his services for the services of the other. Both services had about the same value. By trading them directly, they didn't pay VAT or tax on income, as no money or even goods were involved here. That wasn't the reason for the barter, but it's an interesting aspect. 

I'm not pushing this behaviour, but it makes me wonder why there's not more people doing this, as it is an easy way to save money by leaving out money and thus taxes. AFAIK, this is legal, or at least a 'grey area'. I suppose in most countries some law exists to prevent this happening on a large scale, but it would be impossible to enforce it everywhere or on a small scale. Especially since goods can still be valued in terms of money, but it is much harder to do so with services. And their presence and traceability is volatile, unlike with goods.

I live in a rather small village where locals often (have to) make use of each others service, often requiring the service more than once. Taxes and VAT are high here in the Netherlands, so it would make a significant difference. I'd expect them to barter the service to save money, but they just pay by the bill. I did witness two people bartering once, but never before. I haven't heard it to be common in other modern countries either. Why is it not more common?
The main likely reasons why barter is not more common are:


The inconvenience of having to find another party who both offers what you want and wants what you offer.  
Even if such a party can be found, the possible complexity of negotiating a "fair" transaction (eg I'll do your electrical job if you'll clean my windows monthly for the next 3 months).
I don't want to encourage it, but for those seeking to evade tax, the comparative ease in many circumstances of doing so via a normal monetary transaction, but with payment in cash.


A further point is that most countries with VAT have a significant "VAT threshold", that is, a minimum value of annual sales at which businesses are required to register for VAT and charge VAT (where applicable) on their sales.  In the UK, for example, the threshold is currently £85,000. So an individual could provide services not exceeding that amount in any year and would not have to charge VAT.  If two such individuals were to enter into a barter arrangement, there would be no VAT saving. The Netherlands is atypical in that its VAT threshold is unusually low: 1,345 Euros (see here, table on p 2).