I found this guitar ("guitarra de calidad" of hermanos Godvinez mod. G 705) at a local shop. I play electric so I'm not an expert of classical guitars. The price is affrodable, but I'm not sure if worth while buying it. Considering it has been left without a string could have it sustained any damage? Could you give me some advice on how to examine the guitar for possible flaws? and in case what strings to select for this particular instrument.
I'd take someone along more familiar with classical guitars, unless they're selling it for less than $£€ 50, in which case you could take a punt.
That one looks like it's had a hard life, mainly one of neglect rather than actual intentional mis-treatment; owned by someone who didn't care about it at all. It has the wrong strings on - ball-end instead of tied. They were wound on by a 4-year-old, or someone with absolutely no clue or care as to how to string a guitar.
Anything this badly treated could also have been left in the sun, or a cold cellar or attic. The owner wouldn't even have thought twice about that.
If you go to see it by yourself, check the neck is not twisted - sight along it from the body end. Test the relief on the neck by pressing one string at 1st & last fret & see what the gap is like halfway between. It will possibly be a bit tight as it's only got 5 strings on. You'd need an expert to decide if it's absolutely too tight, but I'd expect some clearance if not much. The string should sound if struck gently.
If you could throw a cat through the gap, leave.
Check the overall body condition. It looks more neglected than mis-treated, but check for cracks in the varnish at significant stress points, neck-body joint, headstock etc. The odd little ding or scratch won't make any appreciable difference, but one drop could potentially start a stress-detach event later in its life.
As it has what looks like a security tag on it so possibly in a store, see what guarantee the seller will give against hidden damage showing up soon after it's properly strung. Unless you take a torch & dentist's mirror with you, inspecting the inside for strut damage etc is not going to be easy.
For the 'best', easy-to-acquire strings, just take it to a music shop & ask the assistant - or just ring up if covid restrictions prevent you attending in person. They'll either have a favourite, or just know the ones the store sells the most of for that guitar type. Either get them to string it, or you'll have to google how to tie plain ended strings.
This looks like a decent pictorial guide - note that not only do you need to get the knot right, but the machine-head windings all need to line up as closely to straight through the nut as you can get them. …and trim the ends so it doesn't look like it was attacked by a bored spider ;)
I think others believe it's been more mistreated than I see in the pictures. Clearly it was last restrung by someone who doesn't know how, but that shouldn't harm the instrument and I'd likely restring it first thing anyway, but I'm seeing no obvious damage and straight reflections of the overhead lights.
Beyond looking down the neck for straightness, tune it up and fret it up the neck to check for dead frets and such. Because of lack of tension, there is no truss rod, so if the guitar has problems, there's little you can do to fix it without steam and glue and luthiery. Also, listen for rattles when playing; there might be loose braces.
I wouldn't expect a great guitar from the looks, but I wouldn't expect it to be bad.
Check the intervals through all the fretboard with your ears and an electric tuner: the majority of cheep and expensive bad damaged guitars do not build/form intervals correctly and you can`t change it like on electric guitar. Good guitars are crafted with hands of a modern Stradivary guy, not by the robots from a China military conversion craftshop. However monetary price is not always a quality metrics. All the parts of a musical instrument matter.