Well, over the years people here in PY and NL hired my services for connecting their home to their ISP, but also to fix the mess of the previous "tech", whether that may have been themselves, the kid next door, a niece/nephew etc.
Double NAT I always encounter. Lots of overlapping signals/channels too. Shoddy UTP cabling too (with non-standard lengths of cable), cable modems attached to rusted coax connectors, (very) old model coax connectors provided by the cable company years ago. Sometimes even the cardinal sin, a signal amplifier between coax connector and cable modem. All big no-no's and things you can rather easily fix yourself.
In NL cable companies (still) operate under similar monopoly rules/regulations as the US. However, they do mention which type/model of coax connector you must use in combination with their modem. And no, even if a new but different type/model connector is installed by the owner of the building, you will still get a crappy internet connection. Those connectors are really not made all equal, even though they appear to look the same. Shoddy workmanship with the correct type/model of connector? Yep, another way to get a (very) crappy internet connection. If you get a visit from a tech in NL, that is always the first thing they check.
Of course, it is possible that there is a problem getting internet to the building over the remainder from the network of the cable ISP. And that is indeed something they will need to fix. However, the "last mile" between ISP and a home is more often the cause of crappy internet connections. To clarify: in NL all lines for coax, electricity, telephone, gas and water to a home are put into the ground. Makes all those networks extremely reliable. And that includes internet through cable modems, glass fiber and copper phone-lines. Cable companies normally use 1 small, grey metal box per street to provide each house with a coax signal. And as long as nobody crashes their car/truck into those, they work well.
The last house I called home in NL, was a house that was already 50 years old. Still, after the cable company upgraded their little grey box for the neighborhood and me replacing the coax connector for a supported model, my cable internet connection worked flawlessly. And that was over 20 year old coax cable between the grey box in the street and the house. Keeping the cable modem as close as possible to the coax connector is also very helpful and from that point on using a CAT5e UTP cable to a router/switch physically about 10 meters removed from the coax connector (but I needed almost 25 meters of UTP cable to work it out of sight).
In four years I had no issues with that setup and then I became an expat in PY...where all lines for electricity, telephone, coax and fiber are above ground. Very unreliable. So much so, that most ISPs use WiMax for interconnecting neighborhoods instead. Such service is also available for normal residences too. It was a pleasant surprise to find out that WiMax is practically as reliable as a cabled network. Especially compared with the misery that are consumer grade WiFi devices.
Sorry for another long rant.