Any advice? Really? OK, here goes: It's been off the road since 2009, the stated odometer reading in the ad would equate to around 53000 miles yet the last test certificate showed 70 odd thousand, but that said, I have a few speedometers for these and I've yet to sell one to somebody who wanted to maintain continuity, so maybe it's a mistake or a new speedo head has been fitted.
If the heater is that rusty, what state is the chassis in? Yes, these are galvanised but I've seen Rialtos and Robins of this era whose zince had fallen off within months and whose chassis had then rotted out prematurely. Workers from Two Gates would carry these chassis from their leaky, mud floored shed, or "factory" if you're being generous, over the lights to the other side of the main road where the galvanisers' premises were located. I recall seeing a spectacularly rotten 1993 Robin LE in Penguin, the then local Reliant dealer's workshop. The car was supplied new to its local keeper in the Autumn of '93, the chassis had all but dissolved by a year later thanks to poor pickling prior to dipping. But that's easy to check and any still on their factory chassis might be fine if they weren't processed on a bad day.
After so long off the road, the engine could well be seized, or the car may have been taken out of service prematurely as a result of overheating or gearbox detent spring failure, among other common faults.
Engines with questionable head gasket health can generally be saved. Some will give up the studs' hold on the head with no trouble, others are reluctant to shift but Reliant specialists have a tool that can force the head off and the block is rarely beyond saving, but occasionally, the cylinders, which sit in the all aluminium block on a bead of sealant and the odd washer to set the distance by which the liners protrude above the block. This is often the source of coolant finding its way into the engine oil. Oil pressure relief valves can fail as their cast iron seat was set in the block with a dob of Araldite by the factory, this glue would fail and the seat would leech oil past the valve, giving very low pressure readings, later, one-piece relief valves which came with their own cassette sealed at the block with an o ring, are easily swapped in, but they're scarce now and I'm not parting with my last two spare, n/o/s ones - just in case!
So check, in no particular sequence:
Chassis condition, including the steel tubular frame that comes through the body behind the door and is clamped to the chassis, an area that isn't galvanised so most unrestored small Reliants are blessed with bodies that aren't quite as securely attached to their chassis as they should be. No great problem if the body is either peeled apart where the inner and outer panels meet, or a hole is cut in the B pillar for access.
Engine running temperature and oil pressure.
Later Robins which have a rear wheel fitted on the front! Very occasionally, I've met with this. It can make the car pull to one side, but just be aware that mini wheels are for the rear, the front wheel has more inset. All easy enough to address, but for the rarity of wheels these days.
Body condition.GRP may not corrode as steel does, so that's a good thing, but when anything made out of the stuff has been left outside for that long, it pays to check for areas where the surface has been broken, say in a minor scrape or when hitting a wall, etc. Any compromised areas can and do absorb moisture and, when these dry out again, the matting tends to crumble. Again, easy enough to identify but can be expensive to fix, though as body repairs can be made with everything from Elastoplasts to sticky tape and will look ok for a while after a quick splash of Crown Plus Two, it's worth doing properly.
MOT test station availability! A few years ago, it was easy to find a place that would test three wheelers, now very few testing venues cater for them, so either buy a pre-1980 example and soak up the extra cost of insuring an MOT exempt car that hasn't been tested (many insurers add extra to the price of a policy for a car that's taken advantage of the exemption, the chiselling twunts). or prepare to have to shove it in the back of a van and take it for a road trip to a tricycle-friendly place. In practice, many testing stations
could test these by getting themselves a bit of paperwork and gaining the right to do this, as the brake test can be performed with the Tapley decellerometer in the car rather than on the rollers and the front wheel can be supported on the jacking beam, but demand isn't exactly high.
It may well be worth considering as they are a fun thing to drive when fully working, but without wishing to talk down values; bubonic plague is rare too and that's rarely overvalued in sales ads!
If its chassis and all that stuff checks out and the buyer joins a club that caters for these things, then it can be rescued and they're easy enough to work on, but at
that price? Hmm..