Buying train tickets in Spain online - safe?

Sure, not aware of any problems.

I've heard complaints about Renfe, as well as CP in Portugal and Trenitalia in Italy. Yet, I've bought from all three in the past with no issues. Go for it.

It's safe...if you can get it to work.

Just booking tickets on the Renfe site now. It's the Spanish train company, so no reason to think it's not safe. I always try to book direct rather than through third party sites, so it's my preference.

I use Trainline and it works fine.

The time I used it everything was fine. No problems and it was as safe as any other website selling tickets.

One problem with Renfe is that it claims it puts tickets on regular trains for sale 60 days in advance of the travel date and 90 days or more for high-speed trains.
In reality, Renfe fails on both of the timelines it claims it goes by.
We just returned from Spain two days ago on Saturday. The final outstanding bookings for this 5-week trip were train tickets from Madrid to San Sebastián/Donostia and San Sebastian/Donostia to Barcelona. Renfe has no competition on these two routes and only has one high-speed train departing in the morning for each of these routes. Other train ticket resellers such as The Trainline and Rail Europe can only sell tickets on Renfe trains after Renfe releases the train schedules and pricing on its computer system which both the Trainline and RailEurope are linked up to.
Here’s what happened in the case of the Madrid to San Sebastián/ Donostia train tickets
In more than 25 years f buying non-refundable and non-exchangeable train tickets, I have never missed a train or had any other problem. I saw that this ticket type for the one daily high-speed train departing from Madrid for San Sebastián at 8:43am was offered for as little as €19 ( or close to $21). on many other dates. I figured that’s close to what I would be paying if I acted quickly when they were first put on sale. With all our hotels pre-booked 4 months in advance, we were locked into traveling from Madrid to San Sebastián/Donostia on September 12,

After fastidiously checking the Renfe website several times each day beginning in mid-July, I finally saw the tickets go up for sale weeks later on Renfe’s website on August 5. But instead of costing $21, Renfe put them up for sale 38 days prior ( not 60 days which Renfe claims it does). beginning at $74 each. Concerned that the tickets could sell out and believing the price likely would rise, I bought the two non-refundable non-exchangeable tickets for $149.43 directly on Renfe’s website.
The very next day on August 6 and for many days after, Renfe had the tickets priced at $21.
I never saw the tickets for sale for $74 again—only on the first day they went on sale.
In my 25 years of buying train tickets, I’m used to prices rising the closer you get to the date of travel. And I have never seen a national train company, such as Spain’s Renfe, put tickets for sale on day 1, and then slash the price by 65% on day 2 and onward.

There is no explanation I can think of ( other than predatory pricing) that can account for this. Dynamic pricing does not work this way.
If you watch other train routes where Renfe has competition from Ouigo or Iryo, train tickets are quite reasonable. If you look at routes where Renfe has no competition such as Seville to Granada, and as it did for decades with the Madrid to Barcelona route—ticket prices skyrocket.

I used Renfe without any issues.

Thank you everyone. I went ahead and booked tickets using Renfe. It was very straightforward so I’m hoping that catching the train at the station will be the same. Happy travels to all!

I have been using train line to book Renfre and Iryo. Easy to use and have had no problems

Until recently, RENFE was the only train company operating in Spain. Now Iryo and Avlo (Renfe's low cost company) also operate throughout Spain. Travelling by train in Spain is very comfortable and it is totally safe to buy online on their websites. Trains, except for some occasional exceptions, are very punctual in Spain.