This isn't a good time to get a clear answer. The combination of Covid, Brexit and changes to the way VAT is collected on imports have made trade and costs uncertain at the moment. The VAT system is still settling in, while leaving the EU changes the UK's trade relationship with almost everyone, and it's a work in progress.
Personally, I wouldn't be happy to import anything on a very tight budget. Though ebay and others seem to be a doing a good job, the system isn't bedded down yet, and there's a risk it will go wrong, as in Matt's example. ebay cancelled his transaction probably because a mistake made the sale unprofitable and because ebay don't want to annoy customers with unexpected extra charges on delivery. Easier to cancel.
Typing in April 2021 I don't think there's a fail-safe guarantee an import buyer won't be charged surprise Duty, VAT, and Handling Charges. So, if unable to afford extra costs on a tight budget I wouldn't buy close to the £135 threshold, where Duty and VAT might both bite. However, as the number of people being charged more on delivery seems low, I would take the risk provided finding the extra money wasn't a painful embarrassment! As always, the world is kindest to folk with muscular bank accounts!
Dave