Should I have a survey ?

Yes, if it gives you peace of mind when confirming your choice of property purchase.

In the overall scheme, it's a relatively small cost, typically a few thousand Euros for a medium size house without particular complications.

If you have a decent knowledge of buildings you might back your own experience. Check first that agent and vendor are comfortable with this before you start banging and poking about. And as a courtesy, perhaps consider first whether you are serious or curious. At BVI we will offer you a choice of English speaking professional surveyors. You pay them in advance and they report to you, not us.

A reasonable alternative if you have a few specific concerns is to get a local builder to express an opinion.
The 'expert' in the bar is usually a very bad idea; in any regard.

As with choosing an agent in whom to place your trust, allow instinct to guide you with a surveyor. Are you comfortable working with this person? Do they communicate clearly and take a genuine interest in what you want?

Ask what they will report on, what is likely to be excluded and that they look at anything of particular concern or interest to you. Ask in advance of the survey!
They will usually report verbally on the day, and follow it up with a written report.
You can quickly focus on getting the property or walking away.

Vendors may be wary of surveys. It isn’t yet common practice in France.
A good agent will reassure a vendor that your investment in a survey is a sign of positive interest, not simply a clumsy attempt to renegotiate the price. Negotiation is a skill of diplomacy and good agents will broker a deal that suits all parties.

This good agent we keep mentioning will point out to you the buyer, property defects known to them.
Don't rely on this; it is highly unlikely to be exhaustive.

See also:
‘Expertise’
Vice-caché

One for the less technical: another pair of feet.